Add basic stacktrace handler using libunwind.

This means we will all have to apt-get install libunwind8-dev on Linux.  Mac comes with everything we need already.

BUG=skia:
R=reed@google.com, mtklein@google.com

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/343583005
diff --git a/gyp/bench.gyp b/gyp/bench.gyp
index 8c81991..a5e0cd6 100644
--- a/gyp/bench.gyp
+++ b/gyp/bench.gyp
@@ -9,11 +9,12 @@
       'target_name': 'bench',
       'type': 'executable',
       'dependencies': [
-        'skia_lib.gyp:skia_lib',
         'bench_timer',
+        'crash_handler.gyp:CrashHandler',
+        'etc1.gyp:libetc1',
         'flags.gyp:flags',
         'jsoncpp.gyp:jsoncpp',
-        'etc1.gyp:libetc1',
+        'skia_lib.gyp:skia_lib',
       ],
       'sources': [
         '../bench/ResultsWriter.cpp',