[Android] Add switch to disable native event batching

content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java

Index: content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java
diff --git a/content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java b/content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java
index d0bcd486ece4adf008e0e52c3139b536ddb9d1e6..6a15a623391b223e6f4244d15a590f0b6d64197a 100644
--- a/content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java
+++ b/content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java
@@ -40,6 +40,7 @@ import android.view.inputmethod.EditorInfo;
 import android.view.inputmethod.InputConnection;
 import android.view.inputmethod.InputMethodManager;
 
+import org.chromium.base.CommandLine;
 import org.chromium.base.ObserverList;
 import org.chromium.base.ObserverList.RewindableIterator;
 import org.chromium.base.TraceEvent;
@@ -59,6 +60,7 @@ import org.chromium.content.browser.input.SelectPopup;
 import org.chromium.content.browser.input.SelectPopupDialog;
 import org.chromium.content.browser.input.SelectPopupDropdown;
 import org.chromium.content.browser.input.SelectPopupItem;
+import org.chromium.content.common.ContentSwitches;
 import org.chromium.content_public.browser.AccessibilitySnapshotCallback;
 import org.chromium.content_public.browser.AccessibilitySnapshotNode;
 import org.chromium.content_public.browser.ActionModeCallbackHelper;
@@ -353,6 +355,9 @@ public class ContentViewCore implements AccessibilityStateChangeListener, Displa
     private float mCurrentTouchOffsetX;
     private float mCurrentTouchOffsetY;
 
+    // True if we want to disable Android native event batching and use compositor event queue.
+    private boolean mShouldRequestUnbufferedDispatch;
+
     // Whether the ContentViewCore requires the WebContents to be fullscreen in order to lock the
     // screen orientation.
     private boolean mFullscreenRequiredForOrientationLock = true;
@@ -584,6 +589,9 @@ public class ContentViewCore implements AccessibilityStateChangeListener, Displa
         mSelectionPopupController.setContainerView(getContainerView());
 
         mWebContentsObserver = new ContentViewWebContentsObserver(this);
+
+        mShouldRequestUnbufferedDispatch = Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP
+                && CommandLine.getInstance().hasSwitch(ContentSwitches.DISABLE_EVENT_BATCHING);
     }
 
     /**
@@ -990,12 +998,16 @@ public class ContentViewCore implements AccessibilityStateChangeListener, Displa
         return sendTouchEvent(event, isTouchHandleEvent);
     }
 
+    @SuppressLint("NewApi")

[chongz, 2017/02/22 21:36:15]

I'm not sure what's the proper way of accessing new APIs, do I simply suppress
the lint or should I add some config?

[aelias_OOO_until_Jul13, 2017/02/22 22:40:51]

It's @TargetApi.  I suggest placing it in a small private method to clarify what
is in the API scope:

@TargetApi(Build.VERSION_CODES.L)
private void requestUnbufferedDispatch(MotionEvent touchDownEvent) {
  mContainerView.requestUnbufferedDispatch(touchDownEvent);
}

[chongz, 2017/02/22 23:08:58]

Done.

     private boolean sendTouchEvent(MotionEvent event, boolean isTouchHandleEvent) {
         TraceEvent.begin("sendTouchEvent");
         try {
             int eventAction = event.getActionMasked();
 
             if (eventAction == MotionEvent.ACTION_DOWN) {
+                if (mShouldRequestUnbufferedDispatch) {
+                    mContainerView.requestUnbufferedDispatch(event);
+                }
                 cancelRequestToScrollFocusedEditableNodeIntoView();
             }