Enable pepper threading by default.

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 284 matching lines @@
       # Enable Web Intents web content registration via HTML element
       # and WebUI managing such registrations.
       'enable_web_intents_tag%': 0,
 
       # Webrtc compilation is enabled by default. Set to 0 to disable.
       'enable_webrtc%': 1,
 
       # PPAPI by default does not support plugins making calls off the main
       # thread. Set to 1 to turn on experimental support for out-of-process
       # plugins to make call of the main thread.
-      'enable_pepper_threading%': 0,
+      'enable_pepper_threading%': 1,
 
       # Enables use of the session service, which is enabled by default.
       # Support for disabling depends on the platform.
       'enable_session_service%': 1,
 
       # Enables theme support, which is enabled by default.  Support for
       # disabling depends on the platform.
       'enable_themes%': 1,
 
       # Uses OEM-specific wallpaper resources on Chrome OS.
@@ skipping 3369 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',
   },
 }