[Android] Add gyp support for multidex.

build/android/main_dex_action.gypi

Index: build/android/main_dex_action.gypi
diff --git a/build/android/main_dex_action.gypi b/build/android/main_dex_action.gypi
new file mode 100644
index 0000000000000000000000000000000000000000..06717ddcff61033f445597296aca597126ba2f36
--- /dev/null
+++ b/build/android/main_dex_action.gypi
@@ -0,0 +1,44 @@
+# Copyright 2015 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.
+
+# This file is meant to be included into an action to provide a rule that
+# generates a list of classes that must be kept in the main dex file.
+#
+# To use this, create a gyp target with the following form:
+#  {
+#    'action_name': 'some name for the action'
+#    'actions': [
+#      'variables': {
+#        'jar_path': 'path to jar',
+#        'output_path': 'output path'
+#      },
+#      'includes': [ 'relative/path/to/main_dex_action.gypi' ],
+#    ],
+#  },
+#
+
+{
+  'message': 'Generating main dex classes list for <(jar_path)',
+  'variables': {
+    'jar_path%': '',
+    'output_path%': '',
+    'main_dex_list_script': '<(DEPTH)/build/android/gyp/main_dex_list.py',
+    'main_dex_rules_path': '<(DEPTH)/build/android/main_dex_classes.flags',
+  },
+  'inputs': [
+    '<(jar_path)',
+    '<(main_dex_list_script)',
+    '<(main_dex_rules_path)',
+  ],
+  'outputs': [
+    '<(output_path)',
+  ],
+  'action': [
+    'python', '<(main_dex_list_script)',
+    '--main-dex-list-path', '<(output_path)',
+    '--android-sdk-tools', '<(android_sdk_tools)',
+    '--main-dex-rules-path', '<(main_dex_rules_path)',
+    '<(jar_path)',
+  ]
+}