Move compositor InputHandler from RenderViewImpl to RenderWidget.

content/browser/renderer_host/render_widget_host_input_event_router.cc

Index: content/browser/renderer_host/render_widget_host_input_event_router.cc
diff --git a/content/browser/renderer_host/render_widget_host_input_event_router.cc b/content/browser/renderer_host/render_widget_host_input_event_router.cc
index 888d7ee4c3d191e145f4cd6c160fa9a2ce93f2d2..cb96ee2baaebbe5c11a0de76ae583bf83fb0c90c 100644
--- a/content/browser/renderer_host/render_widget_host_input_event_router.cc
+++ b/content/browser/renderer_host/render_widget_host_input_event_router.cc
@@ -359,6 +359,10 @@ void RenderWidgetHostInputEventRouter::RouteTouchEvent(
       break;
     case blink::WebInputEvent::TouchEnd:
     case blink::WebInputEvent::TouchCancel:
+      // It might be safer to test active_touches_ and only decrement it if it's
+      // non-zero, since active_touches_ can be reset to 0 in
+      // OnRenderWidgetHostViewBaseDestroyed, and this can happen between the
+      // TouchStart and a subsequent TouchMove/End/Cancel.
       DCHECK(active_touches_);
       active_touches_ -= CountChangedTouchPoints(*event);
       if (!touch_target_.target)