android webview: Keep zoom methods synchronous

android_webview/native/aw_contents.cc

Index: android_webview/native/aw_contents.cc
diff --git a/android_webview/native/aw_contents.cc b/android_webview/native/aw_contents.cc
index 935d643cdc210da27221537197577057727cd894..e4928070dec0e651eb3629d546a45dae57b346bd 100644
--- a/android_webview/native/aw_contents.cc
+++ b/android_webview/native/aw_contents.cc
@@ -1013,6 +1013,13 @@ void AwContents::SetBackgroundColor(JNIEnv* env,
   render_view_host_ext_->SetBackgroundColor(color);
 }
 
+void AwContents::SynchronizeRendererScroll(
+    JNIEnv* env,
+    const base::android::JavaParamRef<jobject>& obj) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  browser_view_renderer_.SynchronizeRendererScroll();
+}
+
 void AwContents::OnComputeScroll(JNIEnv* env,
                                  const JavaParamRef<jobject>& obj,
                                  jlong animation_time_millis) {