Remove SK_DISABLE_PIXELREF_LOCKCOUNT_BALANCE_CHECK.

skia/skia_common.gypi

 # Copyright 2013 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.
 
 # This gypi file handles the removal of platform-specific files from the
 # Skia build.
 {
   'includes': [
     # skia_for_chromium_defines.gypi defines skia_for_chromium_defines
     '../third_party/skia/gyp/skia_for_chromium_defines.gypi',
@@ skipping 169 matching lines @@
     # skia uses static initializers to initialize the serialization logic
     # of its "pictures" library. This is currently not used in chrome; if
     # it ever gets used the processes that use it need to call
     # SkGraphics::Init().
     'SK_ALLOW_STATIC_GLOBAL_INITIALIZERS=0',
 
     # Forcing the unoptimized path for the offset image filter in skia until
     # all filters used in Blink support the optimized path properly
     'SK_DISABLE_OFFSETIMAGEFILTER_OPTIMIZATION',
 
-    # Disable this check because it is too strict for some Chromium-specific
-    # subclasses of SkPixelRef. See bug: crbug.com/171776.
-    'SK_DISABLE_PIXELREF_LOCKCOUNT_BALANCE_CHECK',
-
     'IGNORE_ROT_AA_RECT_OPT',
 
     'SK_IGNORE_BLURRED_RRECT_OPT',
 
     'SK_IGNORE_QUAD_RR_CORNERS_OPT',
 
     # this flag forces Skia not to use typographic metrics with GDI.
     'SK_GDI_ALWAYS_USE_TEXTMETRICS_FOR_FONT_METRICS',
 
     'SK_DEFAULT_FONT_CACHE_LIMIT=<(default_font_cache_limit)',
@@ skipping 12 matching lines @@
   # re-export if they include Skia headers in their public headers.
   'all_dependent_settings': {
     'include_dirs': [
       '..',
       'config',
     ],
   },
 
   'msvs_disabled_warnings': [4244, 4267, 4341, 4345, 4390, 4554, 4748, 4800],
 }