Start using 20.0.0 of Android build tools.

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 1600 matching lines @@
           'variables': {
             # Unfortunately we have to use absolute paths to the SDK/NDK because
             # they're passed to ant which uses a different relative path from
             # gyp.
             'android_ndk_root%': '<!(cd <(DEPTH) && pwd -P)/third_party/android_tools/ndk/',
             'android_ndk_experimental_root%': '<!(cd <(DEPTH) && pwd -P)/third_party/android_tools/ndk_experimental/',
             'android_sdk_root%': '<!(cd <(DEPTH) && pwd -P)/third_party/android_tools/sdk/',
             'android_host_arch%': '<!(uname -m)',
             # Android API-level of the SDK used for compilation.
             'android_sdk_version%': '19',
-            'android_sdk_build_tools_version%': '19.0.0',
+            'android_sdk_build_tools_version%': '20.0.0',
             'host_os%': "<!(uname -s | sed -e 's/Linux/linux/;s/Darwin/mac/')",
           },
           # Copy conditionally-set variables out one scope.
           'android_ndk_root%': '<(android_ndk_root)',
           'android_sdk_root%': '<(android_sdk_root)',
           'android_sdk_version%': '<(android_sdk_version)',
           'android_stlport_root': '<(android_ndk_root)/sources/cxx-stl/stlport',
           'host_os%': '<(host_os)',
 
           'android_sdk%': '<(android_sdk_root)/platforms/android-<(android_sdk_version)',
@@ skipping 3984 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',
   },
 }