Isolate check_internal.py to the .gypi files that need it.

google_apis/determine_use_official_keys.gypi

+# Copyright (c) 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.
+
+# Include this .gypi in your target to dynamically set the
+# use_official_google_api_keys variable (unless it is already
+# explicitly set) and the associated preprocessor define.
+
+{
+  'variables': {
+    'variables': {
+      # See documentation of this variable in //build/common.gypi.
+      'use_official_google_api_keys%': 2,
+    },
+
+    # Copy conditionally-set variables out one scope.
+    'use_official_google_api_keys%': '<(use_official_google_api_keys)',
+
+    'conditions': [
+      # If use_official_google_api_keys is already set (to 0 or 1), we
+      # do none of the implicit checking.  If it is set to 1 and the
+      # internal keys file is missing, the build will fail at compile
+      # time.  If it is set to 0 and keys are not provided by other
+      # means, a warning will be printed at compile time.
+      ['use_official_google_api_keys==2', {
+          'use_official_google_api_keys%':
+            '<!(python <(DEPTH)/google_apis/build/check_internal.py <(DEPTH)/google_apis/internal/google_chrome_api_keys.h)',
+        }],
+    ]
+  },
+
+  'conditions': [
+    ['use_official_google_api_keys==1', {
+        'defines': ['USE_OFFICIAL_GOOGLE_API_KEYS=1'],
+      }],
+  ],
+}