[Android] Add gn support for multidex.

build/android/gyp/apkbuilder.py

Index: build/android/gyp/apkbuilder.py
diff --git a/build/android/gyp/apkbuilder.py b/build/android/gyp/apkbuilder.py
index 4f947642dcd3a3a63fcaf6925bfedcc0a6a036f5..7e0ce2303dc31f6b7ac3677a325aab3a3ef1b9b5 100755
--- a/build/android/gyp/apkbuilder.py
+++ b/build/android/gyp/apkbuilder.py
@@ -155,7 +155,12 @@ def main(args):
           apk.writestr('lib/%s/%s' % (options.android_abi, name), ':)',
                        zipfile.ZIP_STORED)
         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')
 
         if options.emma_device_jar:
           # Add EMMA Java resources to APK.