Add gclient hook to download SDK extras on bots.

DEPS

 # This file is used to manage the dependencies of the Chromium src repo. It is
 # used by gclient to determine what version of each dependency to check out, and
 # where.
 #
 # For more information, please refer to the official documentation:
 #   https://sites.google.com/a/chromium.org/dev/developers/how-tos/get-the-code
 #
 # When adding a new dependency, please update the top-level .gitignore file
 # to list the dependency's destination directory.
 #
@@ skipping 538 matching lines @@
     # Done in lieu of building the toolchain from scratch as it can take
     # anywhere from 30 minutes to 4 hours depending on platform to build.
     'name': 'nacltools',
     'pattern': '.',
     'action': [
         'python',
         'src/build/download_nacl_toolchains.py',
     ],
   },
   {
+    # This downloads SDK extras and puts them in the
+    # third_party/android_tools/sdk/extras directory on the bots. Developers
+    # need to manually install these packages and accept the ToS.
+    'name': 'sdkextras',
+    'pattern': '.',
+    # Make sure to add package to .gitignore in third_party/android_tools.
+    'action': ['python', 'src/build/download_sdk_extras.py',
+               'google_google_play_services_21.0.0'],
+  },
+  {
     # Downloads the Debian Wheezy sysroot to chrome/installer/linux if needed.
     # This sysroot updates at about the same rate that the chrome build deps
     # change. This script is a no-op except for linux users who are doing
     # official chrome builds.
     'name': 'sysroot',
     'pattern': '.',
     'action': [
         'python',
         'src/chrome/installer/linux/sysroot_scripts/install-debian.wheezy.sysroot.py',
         '--linux-only',
@@ skipping 216 matching lines @@
     # corresponding .py files have already been deleted.
     'name': 'remove_stale_pyc_files',
     'pattern': 'src/tools/.*\\.py',
     'action': [
         'python',
         'src/tools/remove_stale_pyc_files.py',
         'src/tools',
     ],
   },
 ]