Enable extended debugging symbols to including better tracking.

build/common.gypi

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 3543 matching lines @@
             },
             'defines': [
               '_DEBUG',
             ],
             'cflags': [
               '-O>(debug_optimize)',
               '-g',
               '-gdwarf-4',
             ],
             'conditions' : [
+              ['fastbuild==0', {
+                'cflags': [
+                  '-fvar-tracking-assignments', '-fvar-tracking',

[Lei Zhang, 2014/09/23 23:58:05]

Do we need to explicitly pass -fvar-tracking? The man page says it's "enabled by
default when compiling with optimization ..." We seem to meet all the
requirements.

+                ],
+              }],
               ['OS=="android"', {
                 'ldflags': [
                   # Warn in case of text relocations.
                   '-Wl,--warn-shared-textrel',
                 ],
               }],
               ['OS=="android" and android_full_debug==0', {
                 # Some configurations are copied from Release_Base to reduce
                 # the binary size.
                 'variables': {
@@ skipping 2205 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }