[Android] Add gn support for multidex.

build/android/gyp/apkbuilder.py

 #!/usr/bin/env python
 #
 # Copyright (c) 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.
 
 """Adds the code parts to a resource APK."""
 
 import argparse
 import itertools
@@ skipping 128 matching lines @@
         _AddAssets(apk, options.assets, disable_compression=False)
         _AddAssets(apk, options.uncompressed_assets, disable_compression=True)
         for path in native_libs:
           basename = os.path.basename(path)
           apk.write(path, 'lib/%s/%s' % (options.android_abi, basename))
         if options.create_placeholder_lib:
           # Make it non-empty so that its checksum is non-zero and is not
           # ignored by md5_check.
           apk.writestr('lib/%s/libplaceholder.so' % options.android_abi, ':-)')
         if options.dex_file:
-          apk.write(options.dex_file, 'classes.dex')
+          if options.dex_file.endswith('.zip'):
+            with zipfile.ZipFile(options.dex_file, 'r') as dex_zip:
+              for dex in (d for d in dex_zip.namelist() if d.endswith('.dex')):
+                apk.writestr(dex, dex_zip.read(dex))
+          else:
+            apk.write(options.dex_file, 'classes.dex')
 
       shutil.move(tmp_apk, options.output_apk)
     finally:
       if os.path.exists(tmp_apk):
         os.unlink(tmp_apk)
 
   build_utils.CallAndWriteDepfileIfStale(
       on_stale_md5,
       options,
       input_paths=input_paths,
       input_strings=input_strings,
       output_paths=[options.output_apk])
 
 
 if __name__ == '__main__':
   main(sys.argv[1:])