diff --git a/experimental/benchtools/rebase.py b/experimental/benchtools/rebase.py
index 85290d7..f542454 100755
--- a/experimental/benchtools/rebase.py
+++ b/experimental/benchtools/rebase.py
@@ -32,9 +32,6 @@
 # Google Storage bench file prefix.
 GS_PREFIX = 'gs://chromium-skia-gm/perfdata'
 
-# List of Perf platforms we want to process. Populate from expectations/bench.
-PLATFORMS = []
-
 # Regular expression for matching githash data.
 HA_RE = '<a href="/skia/\+/([0-9a-f]+)">'
 HA_RE_COMPILED = re.compile(HA_RE)
@@ -88,17 +85,61 @@
     return True
   return False
 
-def calc_expectations(p, h, gs_dir, exp_dir, repo_dir):
+def get_expectations_dict(f):
+  """Given an expectations file f, returns a dictionary of data."""
+  # maps row_key to (expected, lower_bound, upper_bound) float tuple.
+  dic = {}
+  for l in open(f).readlines():
+    line_parts = l.strip().split(',')
+    if line_parts[0].startswith('#') or len(line_parts) != 5:
+      continue
+    dic[','.join(line_parts[:2])] = (float(line_parts[2]), float(line_parts[3]),
+                                     float(line_parts[4]))
+
+  return dic
+
+def calc_expectations(p, h, gs_dir, exp_dir, repo_dir, extra_dir, extra_hash):
   exp_filename = 'bench_expectations_%s.txt' % p
+  exp_fullname = os.path.join(exp_dir, exp_filename)
   proc = subprocess.Popen(['python', 'skia/bench/gen_bench_expectations.py',
-      '-r', h, '-b', p, '-d', os.path.join(gs_dir, p), '-o',
-          os.path.join(exp_dir, exp_filename)],
+      '-r', h, '-b', p, '-d', os.path.join(gs_dir, p), '-o', exp_fullname],
               stdout=subprocess.PIPE)
   out, err = proc.communicate()
   if err:
     print 'ERR_CALCULATING_EXPECTATIONS: ' + err
     return False
   print 'CALCULATED_EXPECTATIONS: ' + out
+  if extra_dir:  # Adjust data with the ones in extra_dir
+    print 'USE_EXTRA_DATA_FOR_ADJUSTMENT.'
+    proc = subprocess.Popen(['python', 'skia/bench/gen_bench_expectations.py',
+        '-r', extra_hash, '-b', p, '-d', os.path.join(extra_dir, p), '-o',
+            os.path.join(extra_dir, exp_filename)],
+                stdout=subprocess.PIPE)
+    out, err = proc.communicate()
+    if err:
+      print 'ERR_CALCULATING_EXTRA_EXPECTATIONS: ' + err
+      return False
+    extra_dic = get_expectations_dict(os.path.join(extra_dir, exp_filename))
+    output_lines = []
+    for l in open(exp_fullname).readlines():
+      parts = l.strip().split(',')
+      if parts[0].startswith('#') or len(parts) != 5:
+        output_lines.append(l.strip())
+        continue
+      key = ','.join(parts[:2])
+      if key in extra_dic:
+        exp, lb, ub = (float(parts[2]), float(parts[3]), float(parts[4]))
+        alt, _, _ = extra_dic[key]
+        avg = (exp + alt) / 2
+        # Keeps the extra range in lower/upper bounds from two actual values.
+        new_lb = min(exp, alt) - (exp - lb)
+        new_ub = max(exp, alt) + (ub - exp)
+        output_lines.append('%s,%.2f,%.2f,%.2f' % (key, avg, new_lb, new_ub))
+      else:
+        output_lines.append(l.strip())
+    with open(exp_fullname, 'w') as f:
+      f.write('\n'.join(output_lines))
+
   repo_file = os.path.join(repo_dir, 'expectations', 'bench', exp_filename)
   if (os.path.isfile(repo_file) and
       filecmp.cmp(repo_file, os.path.join(exp_dir, exp_filename))):
@@ -125,13 +166,16 @@
   os.chdir(old_cwd)
   return status
 
-def git_commit_expectations(repo_dir, exp_dir, update_li, h, commit):
-  commit_msg = """manual bench rebase after %s
+def git_commit_expectations(repo_dir, exp_dir, update_li, h, commit,
+                            extra_hash):
+  if extra_hash:
+    extra_hash = ', adjusted with ' + extra_hash
+  commit_msg = """manual bench rebase after %s%s
 
 TBR=robertphillips@google.com
 
 Bypassing trybots:
-NOTRY=true""" % h
+NOTRY=true""" % (h, extra_hash)
   old_cwd = os.getcwd()
   os.chdir(repo_dir)
   upload = ['git', 'cl', 'upload', '-f', '--bypass-hooks',
@@ -175,7 +219,14 @@
     return
   parser = argparse.ArgumentParser()
   parser.add_argument('--githash',
-                      help='Githash prefix (7+ chars) to rebaseline to.')
+                      help=('Githash prefix (7+ chars) to rebaseline to. If '
+                            'a second one is supplied after comma, and it has '
+                            'corresponding bench data, will shift the range '
+                            'center to the average of two expected values.'))
+  parser.add_argument('--bots',
+                      help=('Comma-separated list of bots to work on. If no '
+                            'matching bots are found in the list, will default '
+                            'to processing all bots.'))
   parser.add_argument('--commit', action='store_true',
                       help='Whether to commit changes automatically.')
   args = parser.parse_args()
@@ -193,30 +244,54 @@
     print 'Updated this script from repo; please run again.'
     return
 
+  all_platforms = []  # Find existing list of platforms with expectations.
   for item in os.listdir(os.path.join(d, 'skia/expectations/bench')):
-    PLATFORMS.append(
+    all_platforms.append(
         item.replace('bench_expectations_', '').replace('.txt', ''))
 
+  platforms = []
+  # If at least one given bot is in all_platforms, use list of valid args.bots.
+  if args.bots:
+    bots = args.bots.strip().split(',')
+    for bot in bots:
+      if bot in all_platforms:  # Filters platforms with given bot list.
+        platforms.append(bot)
+  if not platforms:  # Include all existing platforms with expectations.
+    platforms = all_platforms
+
   if not args.githash or len(args.githash) < 7:
     raise Exception('Please provide --githash with a longer prefix (7+).')
+  githashes = args.githash.strip().split(',')
+  if len(githashes[0]) < 7:
+    raise Exception('Please provide --githash with longer prefixes (7+).')
   commit = False
   if args.commit:
     commit = True
-  rebase_hash = args.githash[:7]
+  rebase_hash = githashes[0][:7]
+  extra_hash = ''
+  if len(githashes) == 2:
+    extra_hash = githashes[1][:7]
   hashes = get_git_hashes()
   short_hashes = [h[:7] for h in hashes]
-  if rebase_hash not in short_hashes:
-    raise Exception('Provided --githash not found in recent history!')
+  if (rebase_hash not in short_hashes or
+      (extra_hash and extra_hash not in short_hashes) or
+      rebase_hash == extra_hash):
+    raise Exception('Provided --githashes not found, or identical!')
+  if extra_hash:
+    extra_hash = hashes[short_hashes.index(extra_hash)]
   hashes = hashes[:short_hashes.index(rebase_hash) + 1]
   update_li = []
 
   ts_str = '%s' % time.time()
   gs_dir = os.path.join(d, 'gs' + ts_str)
   exp_dir = os.path.join(d, 'exp' + ts_str)
+  extra_dir = os.path.join(d, 'extra' + ts_str)
   clean_dir(gs_dir)
   clean_dir(exp_dir)
-  for p in PLATFORMS:
+  clean_dir(extra_dir)
+  for p in platforms:
     clean_dir(os.path.join(gs_dir, p))
+    clean_dir(os.path.join(extra_dir, p))
     hash_to_use = ''
     for h in reversed(hashes):
       li = get_gs_filelist(p, h)
@@ -230,18 +305,23 @@
         print 'DOWNLOAD BENCH FAILED %s/%s' % (p, h)
         break
     if hash_to_use:
-      if calc_expectations(p, h, gs_dir, exp_dir, repo_dir):
+      if extra_hash and download_gs_files(p, extra_hash, extra_dir):
+        print 'Copied extra data %s/%s' % (p, extra_hash)
+        if calc_expectations(p, h, gs_dir, exp_dir, repo_dir, extra_dir,
+                             extra_hash):
+          update_li.append('bench_expectations_%s.txt' % p)
+      elif calc_expectations(p, h, gs_dir, exp_dir, repo_dir, '', ''):
         update_li.append('bench_expectations_%s.txt' % p)
   if not update_li:
     print 'No bench data to update after %s!' % args.githash
   elif not git_commit_expectations(
-      repo_dir, exp_dir, update_li, args.githash[:7], commit):
+      repo_dir, exp_dir, update_li, rebase_hash, commit, extra_hash):
     print 'ERROR uploading expectations using git.'
   elif not commit:
     print 'CL created. Please take a look at the link above.'
   else:
     print 'New bench baselines should be in CQ now.'
-  delete_dirs([gs_dir, exp_dir])
+  delete_dirs([gs_dir, exp_dir, extra_dir])
 
 
 if __name__ == "__main__":