Resend unconsumed scroll update from guest back to embedder (WebView Scroll Bubble).

content/browser/renderer_host/render_widget_host_impl.cc

Index: content/browser/renderer_host/render_widget_host_impl.cc
diff --git a/content/browser/renderer_host/render_widget_host_impl.cc b/content/browser/renderer_host/render_widget_host_impl.cc
index 9e6a414ce5a8fc5fc7dfd96d47598f6ead6a59f6..7050eb275df57250cd0e8555fb4b59ed260e65c4 100644
--- a/content/browser/renderer_host/render_widget_host_impl.cc
+++ b/content/browser/renderer_host/render_widget_host_impl.cc
@@ -172,6 +172,7 @@ RenderWidgetHostImpl::RenderWidgetHostImpl(RenderWidgetHostDelegate* delegate,
       pending_mouse_lock_request_(false),
       allow_privileged_mouse_lock_(false),
       has_touch_handler_(false),
+      is_in_gesture_scroll_(false),
       next_browser_snapshot_id_(1),
       owned_by_render_frame_host_(false),
       is_focused_(false),
@@ -979,6 +980,15 @@ void RenderWidgetHostImpl::ForwardGestureEventWithLatencyInfo(
   if (IgnoreInputEvents())
     return;
 
+  if (gesture_event.type == blink::WebInputEvent::GestureScrollBegin) {
+    DCHECK(!is_in_gesture_scroll_);
+    is_in_gesture_scroll_ = true;
+  } else if (gesture_event.type == blink::WebInputEvent::GestureScrollEnd ||
+           gesture_event.type == blink::WebInputEvent::GestureFlingStart) {
+    DCHECK(is_in_gesture_scroll_);
+    is_in_gesture_scroll_ = false;
+  }
+
   if (delegate_->PreHandleGestureEvent(gesture_event))
     return;