Add "envoy" GYP variable for pulling in envoy targets.

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 1471 matching lines @@
 
     # Use brlapi from brltty for braille display support.
     'use_brlapi%': 0,
 
     # Relative path to icu.gyp from this file.
     'icu_gyp_path': '../third_party/icu/icu.gyp',
 
     # IPC fuzzer is disabled by default.
     'enable_ipc_fuzzer%': 0,
 
-
     # Force disable libstdc++ debug mode.
     'disable_glibcxx_debug%': 0,
 
     # Set to 1 to compile with MSE support for MPEG2 TS
     'enable_mpeg2ts_stream_parser%': 0,
 
     # Support ChromeOS touchpad gestures with ozone.
     'use_evdev_gestures%': 0,
 
     # Default ozone platform (if no --ozone-platform flag).
     'ozone_platform%': "",
 
     # Ozone platforms to include in the build.
     'ozone_platform_caca%': 0,
     'ozone_platform_dri%': 0,
     'ozone_platform_egltest%': 0,
     'ozone_platform_gbm%': 0,
     'ozone_platform_ozonex%': 0,
     'ozone_platform_test%': 0,
 
+    # Experiment: http://crbug.com/426914
+    'envoy%': 0,
+
     'conditions': [
       ['buildtype=="Official"', {
         # Continue to embed build meta data in Official builds, basically the
         # time it was built.
         # TODO(maruel): This decision should be revisited because having an
         # official deterministic build has high value too but MSVC toolset can't
         # generate anything deterministic with WPO enabled AFAIK.
         'dont_embed_build_metadata%': 0,
       }],
       # Enable the Syzygy optimization step for the official builds.
@@ skipping 4408 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',
   },
 }