Enable multidex for ChromePublicTests app

chrome/android/BUILD.gn

Index: chrome/android/BUILD.gn
diff --git a/chrome/android/BUILD.gn b/chrome/android/BUILD.gn
index 2f118f0ea97a0a0e74f4e94eb1ed299c679ffbdd..91efb3a829137880349c881cc5973277edcc50f8 100644
--- a/chrome/android/BUILD.gn
+++ b/chrome/android/BUILD.gn
@@ -915,8 +915,11 @@ instrumentation_test_apk("chrome_public_test_apk") {
 
   # The test APK contains code from both the APK under test and the
   # test APK when proguard is enabled. That causes this APK to exceed
-  # the dex limit.
-  enable_multidex = proguard_enabled
+  # the dex limit.  Using android.support.multidex.MultiDexApplication

[jbudorick, 2017/06/06 05:44:59]

This is not the right place for this comment. It'd be fine in the manifest,
though.

[aluo, 2017/06/07 00:52:17]

Done.

+  # to support this case which requires multidex support.  Can't use
+  # BaseChromiumApplication due to BuildConfig.java conflict with
+  # chrome_public_apk.
+  enable_multidex = true

[jbudorick, 2017/06/06 05:44:59]

I don't think this is the right way to ensure MultiDexApplication is included.
Instead, I think you could do this by adding
//third_party/android_tools:android_support_multidex_java to deps above.

[aluo, 2017/06/07 00:52:17]

That wasn't enough, still couldn't find class in debug mode:
android.support.multidex.MultiDexApplication" on path: DexPathList[[zip file
"/system/framework/android.test.runner.jar", zip file
"/data/app/org.chromium.chrome.tests-1.apk"],nativeLibraryDirectories=[/data/app-lib/org.chromium.chrome.tests-1,
/vendor/lib, /system/lib]]
E/AndroidRuntime( 6139): 	at
android.app.LoadedApk.makeApplication(LoadedApk.java:507)
E/AndroidRuntime( 6139): 	at
android.app.ActivityThread.handleBindApplication(ActivityThread.java:4301)
E/AndroidRuntime( 6139): 	at
android.app.ActivityThread.access$1500(ActivityThread.java:135)
E/AndroidRuntime( 6139): 	at
android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
E/AndroidRuntime( 6139): 	at
android.os.Handler.dispatchMessage(Handler.java:102)
E/AndroidRuntime( 6139): 	at android.os.Looper.loop(Looper.java:136)
E/AndroidRuntime( 6139): 	at
android.app.ActivityThread.main(ActivityThread.java:5001)
E/AndroidRuntime( 6139): 	at java.lang.reflect.Method.invokeNative(Native
Method)
E/AndroidRuntime( 6139): 	at java.lang.reflect.Method.invoke(Method.java:515)
E/AndroidRuntime( 6139): 	at
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
E/AndroidRuntime( 6139): 	at
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
E/AndroidRuntime( 6139): 	at dalvik.system.NativeStart.main(Native Method)
E/AndroidRuntime( 6139): Caused by: java.lang.ClassNotFoundException: Didn't
find class "android.support.multidex.MultiDexApplication" on path:
DexPathList[[zip file "/system/framework/android.test.runner.jar", zip file
"/data/app/org.chromium.chrome.tests-1.apk"],nativeLibraryDirectories=[/data/app-lib/org.chromium.chrome.tests-1,
/vendor/lib, /system/lib]]
E/AndroidRuntime( 6139): 	at
dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
E/AndroidRuntime( 6139): 	at
java.lang.ClassLoader.loadClass(ClassLoader.java:497)
E/AndroidRuntime( 6139): 	at
java.lang.ClassLoader.loadClass(ClassLoader.java:457)
E/AndroidRuntime( 6139): 	at
android.app.Instrumentation.newApplication(Instrumentation.java:975)
E/AndroidRuntime( 6139): 	at
android.app.LoadedApk.makeApplication(LoadedApk.java:502)
E/AndroidRuntime( 6139): 	... 11 more


enable_multidex does other extra stuff and appears to be needed for the
MultiDexApplication to work correctly.  Besides, the test target depends on
//base:base_java which already depends on this.

 }
 
 if (enable_vr) {