MouseMove when the mouse is down to signal compositor priority

content/renderer/scheduler/renderer_scheduler_impl.cc

Index: content/renderer/scheduler/renderer_scheduler_impl.cc
diff --git a/content/renderer/scheduler/renderer_scheduler_impl.cc b/content/renderer/scheduler/renderer_scheduler_impl.cc
index 4ffe487b3764faa5abac556b86425a6f6469ee7b..f71892c675b645f0686e3d39a26ad7cee5db81b2 100644
--- a/content/renderer/scheduler/renderer_scheduler_impl.cc
+++ b/content/renderer/scheduler/renderer_scheduler_impl.cc
@@ -120,14 +120,23 @@ void RendererSchedulerImpl::DidCommitFrameToCompositor() {
 }
 
 void RendererSchedulerImpl::DidReceiveInputEventOnCompositorThread(
-    blink::WebInputEvent::Type type) {
+    const blink::WebInputEvent& web_input_event) {
   TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("renderer.scheduler"),
                "RendererSchedulerImpl::DidReceiveInputEventOnCompositorThread");
-  // Ignore mouse events because on windows these can very frequent.
+  // We regard MouseMove events with the left mouse button down as a signsal
+  // that the user is doing something requiring a smooth frame rate.
+  if (web_input_event.type == blink::WebInputEvent::MouseMove &&
+      web_input_event.modifiers & blink::WebInputEvent::LeftButtonDown) {

[picksi, 2015/02/06 09:23:47]

nit: Should we add blink::WebInputEvent::isLeftMouseButton(web_input_event) to
hide the implementation details and to stylistically match the calls to
blink::WebInputEvent::isMouseEventType(web_input_event.type) later on?

If you think that is too heavy handed, it might add to readability to bracket
the bitwise & parameters, as at first glance it looked to me like there were 3
checks in this if.

[alex clarke (OOO till 29th), 2015/02/06 10:12:21]

I can't change WebInputEvent in this patch since that's in the blink repository.
 I've added some brackets instead.

+    UpdateForInputEvent();
+    return;
+  }
+  // Ignore all other mouse events becuase they probably don't signal user
+  // interaction needing a smooth framerate. NOTE isMouseEventType returns false
+  // for mouse wheel events, hence we regard them as user input.
   // Ignore keyboard events because it doesn't really make sense to enter
   // compositor priority for them.
-  if (blink::WebInputEvent::isMouseEventType(type) ||
-      blink::WebInputEvent::isKeyboardEventType(type)) {
+  if (blink::WebInputEvent::isMouseEventType(web_input_event.type) ||
+      blink::WebInputEvent::isKeyboardEventType(web_input_event.type)) {
     return;
   }
   UpdateForInputEvent();