allow skia flags to be specified in a skia file, but reference by chrome's skia_common.gypi

gyp/skia_for_chromium_defines.gypi

+# Copyright 2014 Google Inc.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# This file is included by chrome's skia/skia_common.gypi, and is intended to
+# augment the skia flags that are set there.
+
+{
+  'variables': {
+
+    # These flags will be defined in chromium
+    #
+    # If these become 'permanent', they should be moved into skia_common.gypi
+    #
+    'skia_for_chromium_defines': [
+      'SK_SUPPORT_LEGACY_COMPATIBLEDEVICE_CONFIG=1',
+      'SK_SUPPORT_LEGACY_PUBLICEFFECTCONSTRUCTORS=1',
+      'SK_SUPPORT_LEGACY_COPYTO_CONFIG',
+      'SK_SUPPORT_DEEPCOPYTO_CONFIG',
+    ],
+  },
+}