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

content/renderer/browser_plugin/browser_plugin.cc

Index: content/renderer/browser_plugin/browser_plugin.cc
diff --git a/content/renderer/browser_plugin/browser_plugin.cc b/content/renderer/browser_plugin/browser_plugin.cc
index 48491e6c5861af1089e573f46c264eef382ee4e9..044459f0b7659b1b051bca1d1d63e46745bae9af 100644
--- a/content/renderer/browser_plugin/browser_plugin.cc
+++ b/content/renderer/browser_plugin/browser_plugin.cc
@@ -501,6 +501,18 @@ bool BrowserPlugin::handleInputEvent(const blink::WebInputEvent& event,
   if (guest_crashed_ || !attached())
     return false;
 
+  if (event.type == blink::WebInputEvent::MouseWheel) {
+    auto wheel_event = static_cast<const blink::WebMouseWheelEvent&>(event);
+    if (wheel_event.resendingPluginId == browser_plugin_instance_id_)
+      return false;
+  }
+
+  if (blink::WebInputEvent::isGestureEventType(event.type)) {
+    auto gesture_event = static_cast<const blink::WebGestureEvent&>(event);
+    if (gesture_event.resendingPluginId == browser_plugin_instance_id_)
+      return false;
+  }
+
   if (event.type == blink::WebInputEvent::ContextMenu)
     return true;
 
@@ -518,6 +530,12 @@ bool BrowserPlugin::handleInputEvent(const blink::WebInputEvent& event,
                                                 view_rect_,
                                                 &event));
   GetWebKitCursorInfo(cursor_, &cursor_info);
+
+  // Although we forward this event to the guest, we don't report it as consumed
+  // since other targets of this event in Blink never get that chance either.
+  if (event.type == blink::WebInputEvent::GestureFlingStart)
+    return false;
+
   return true;
 }