Fix Chrome build for RecreateSKPs and CommandBuffer bots for GYP->GN

BUG=skia:5597
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2199273002

Review-Url: https://codereview.chromium.org/2199273002
diff --git a/tools/build_command_buffer.py b/tools/build_command_buffer.py
index 015cdaf..0349419 100755
--- a/tools/build_command_buffer.py
+++ b/tools/build_command_buffer.py
@@ -130,6 +130,25 @@
           error.cmd, chrome_src_dir))
 
   try:
+    subprocess.check_call([gclient, 'runhooks'], cwd=chrome_src_dir)
+  except subprocess.CalledProcessError as error:
+    sys.exit('Error (ret code: %s) calling "%s" in %s' % (
+        error.returncode, error.cmd, chrome_src_dir))
+
+  platform = 'linux64'
+  if sys.platform == 'darwin':
+    platform = 'mac'
+  elif sys.platform == 'win32':
+    platform = 'win'
+  gn = os.path.join(chrome_src_dir, 'buildtools', platform, 'gn')
+  try:
+    subprocess.check_call([gn, 'gen', chrome_target_dir_rel],
+                          cwd=chrome_src_dir)
+  except subprocess.CalledProcessError as error:
+    sys.exit('Error (ret code: %s) calling "%s" in %s' % (
+        error.returncode, error.cmd, chrome_src_dir))
+
+  try:
     subprocess.check_call(['ninja'] + shlex.split(args.extra_ninja_args) +
         ['-C', chrome_target_dir_rel, 'command_buffer_gles2'],
         cwd=chrome_src_dir)