Ensure AreaGestureEventFilter has a valid down event

Because of the way touch events are routed in the layout system, it
is possible for the gesture detectors to occacionally miss events.
This patch checks that events captured by the AreaGestureEventFilter
have a valid down event prior to processing.

Bug: 1026139
Change-Id: I37c26dcc49c36c61290aba7586bdc962238a06eb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2490321
Commit-Queue: Matthew Jones <mdjones@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819908}

chrome/android/java/src/org/chromium/chrome/browser/compositor/layouts/eventfilter/AreaGestureEventFilter.java

@@ -15,6 +15,9 @@ import android.view.MotionEvent;
 public class AreaGestureEventFilter extends GestureEventFilter {
     private final RectF mTriggerRect = new RectF();
 
+    /** Whether a down event has occurred inside of the specified area. */
+    private boolean mHasDownEventInArea;
+
     /**
      * Creates a {@link AreaGestureEventFilter}.
      * @param context       The context to build the gesture handler under.
@@ -66,9 +69,29 @@ public class AreaGestureEventFilter extends GestureEventFilter {
         }
     }
 
+    @Override
+    public boolean onTouchEventInternal(MotionEvent e) {
+        // If the action is up or down, consider it to be a new gesture.
+        if (e.getActionMasked() == MotionEvent.ACTION_UP
+                || e.getActionMasked() == MotionEvent.ACTION_DOWN) {
+            mHasDownEventInArea = false;
+        }
+        return super.onTouchEventInternal(e);
+    }
+
     @Override
     public boolean onInterceptTouchEventInternal(MotionEvent e, boolean isKeyboardShowing) {
+        // If the action is up or down, consider it to be a new gesture.
+        if (e.getActionMasked() == MotionEvent.ACTION_UP
+                || e.getActionMasked() == MotionEvent.ACTION_DOWN) {
+            mHasDownEventInArea = false;
+        }
         if (mTriggerRect.contains(e.getX() * mPxToDp, e.getY() * mPxToDp)) {
+            if (e.getActionMasked() == MotionEvent.ACTION_DOWN) {
+                mHasDownEventInArea = true;
+            } else if (!mHasDownEventInArea) {
+                return false;
+            }
             return super.onInterceptTouchEventInternal(e, isKeyboardShowing);
         }
         return false;