Ensure that we don't report huge mouse movement deltas for mouse enter and leave events.

content/browser/renderer_host/render_widget_host_view_aura.cc

Index: content/browser/renderer_host/render_widget_host_view_aura.cc
diff --git a/content/browser/renderer_host/render_widget_host_view_aura.cc b/content/browser/renderer_host/render_widget_host_view_aura.cc
index e93fd494ddc7155ee6e7dff1db0adbc5df502567..a9250285184169b0462a5f87cf20421b33980960 100644
--- a/content/browser/renderer_host/render_widget_host_view_aura.cc
+++ b/content/browser/renderer_host/render_widget_host_view_aura.cc
@@ -1875,7 +1875,7 @@ void RenderWidgetHostViewAura::OnMouseEvent(ui::MouseEvent* event) {
       }
     }
 
-    ModifyEventMovementAndCoords(&mouse_event);
+    ModifyEventMovementAndCoords(&mouse_event, event);
 
     bool should_not_forward = is_move_to_center_event && synthetic_move_sent_;
     if (should_not_forward) {
@@ -1954,7 +1954,7 @@ void RenderWidgetHostViewAura::OnMouseEvent(ui::MouseEvent* event) {
 
       blink::WebMouseEvent mouse_event = ui::MakeWebMouseEvent(
           *event, base::Bind(&GetScreenLocationFromEvent));
-      ModifyEventMovementAndCoords(&mouse_event);
+      ModifyEventMovementAndCoords(&mouse_event, event);
       if (ShouldRouteEvent(event)) {
         host_->delegate()->GetInputEventRouter()->RouteMouseEvent(
             this, &mouse_event, *event->latency());
@@ -2500,12 +2500,14 @@ void RenderWidgetHostViewAura::FinishImeCompositionSession() {
 }
 
 void RenderWidgetHostViewAura::ModifyEventMovementAndCoords(
-    blink::WebMouseEvent* event) {
+    blink::WebMouseEvent* event,
+    ui::MouseEvent* ui_mouse_event) {

[sky, 2016/10/06 16:33:36]

Make this take a const&, in fact can both args be const& ?

[ananta, 2016/10/06 21:15:18]

Changed ui_mouse_event to be a const ref. The other one can't be as it is
updated below.

Regarding tests, it may be a touch tricky to write a non flaky one, because the
only way I could get this to reliably repro is to hover the mouse right around
the edge of the window border. 

Will see if an interactive test is doable in a future patchset.

   // If the mouse has just entered, we must report zero movementX/Y. Hence we
   // reset any global_mouse_position set previously.
-  if (event->type == blink::WebInputEvent::MouseEnter ||
-      event->type == blink::WebInputEvent::MouseLeave)
-    global_mouse_position_.SetPoint(event->globalX, event->globalY);
+  if (ui_mouse_event->type() == ui::ET_MOUSE_ENTERED ||
+      ui_mouse_event->type() == ui::ET_MOUSE_EXITED) {
+      global_mouse_position_.SetPoint(event->globalX, event->globalY);

[sky, 2016/10/04 18:17:55]

This is the first I've seen of ModifyEventMovementAndCoords. Can you elaborate
on why we need global_mouse_position_ per RWHVA? aura::Env has a
last_mouse_location, can that be used? Screen also has GetCursorScreenPoint(),
which uses GetCursorPos() where as last_mouse_location() is the last mouse
location seen in chrome.

[ananta, 2016/10/04 19:44:52]

The global_mouse_position technically can be possibly replaced with the aura
global. I would prefer to do that in a separate patch.

+  }
 
   // Movement is computed by taking the difference of the new cursor position
   // and the previous. Under mouse lock the cursor will be warped back to the