MSan: change the default value of msan_track_origins to 2.

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 420 matching lines @@
       'tsan_blacklist%': '<(PRODUCT_DIR)/../../tools/memory/tsan_v2/ignores.txt',
 
       # Enable building with MSan (Clang's -fsanitize=memory option).
       # MemorySanitizer only works with clang, but msan=1 implies clang=1
       # See http://clang.llvm.org/docs/MemorySanitizer.html
       'msan%': 0,
       'msan_blacklist%': '<(PRODUCT_DIR)/../../tools/msan/blacklist.txt',
       # Track where uninitialized memory originates from. From fastest to
       # slowest: 0 - no tracking, 1 - track only the initial allocation site, 2
       # - track the chain of stores leading from allocation site to use site.
-      'msan_track_origins%': 1,
+      'msan_track_origins%': 2,
 
       # Enable building with UBSan (Clang's -fsanitize=undefined option).
       # -fsanitize=undefined only works with clang, but ubsan=1 implies clang=1
       # See http://clang.llvm.org/docs/UsersManual.html
       'ubsan%': 0,
       'ubsan_blacklist%': '<(PRODUCT_DIR)/../../tools/ubsan/blacklist.txt',
 
       # Enable building with UBsan's vptr (Clang's -fsanitize=vptr option).
       # -fsanitize=vptr only works with clang, but ubsan_vptr=1 implies clang=1
       'ubsan_vptr%': 0,
@@ skipping 5588 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',
   },
 }