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 5fb48340e8e0d9797cbd848df330f0bc9e38b379..61d35911b3f622d6d51323a5b831fdf77b986d77 100644
--- a/content/browser/renderer_host/render_widget_host_view_aura.cc
+++ b/content/browser/renderer_host/render_widget_host_view_aura.cc
@@ -1819,7 +1819,21 @@ void RenderWidgetHostViewAura::OnKeyEvent(ui::KeyEvent* event) {
 void RenderWidgetHostViewAura::OnMouseEvent(ui::MouseEvent* event) {
   TRACE_EVENT0("input", "RenderWidgetHostViewAura::OnMouseEvent");
 
+  if (event->type() == ui::ET_MOUSE_MOVED) {

[scheib, 2016/10/04 02:01:34]

It seems correct only if a move event will always arrive before an
ENTERED/EXITED. Anything we can say in comments here to explain why we think
this assertion is true?

[ananta, 2016/10/04 02:21:20]

On Windows, a visible window can safely assume that a mouse move will be given
to it for setting the mouse cursor. Given that here we are looking for a mouse
enter or leave, it can be safely assumed that these should be preceded with
mouse moves.

+    last_mouse_position_.set_x(event->x());
+    last_mouse_position_.set_y(event->y());
+  } else if (event->type() == ui::ET_MOUSE_ENTERED ||
+             event->type() == ui::ET_MOUSE_EXITED) {
+    // For mouse entered and exited states the |ui_mouse_event| parameter
+    // contains the location of the cursor which does not work for webpages as
+    // they may track mouse movement deltas. To ensure that the deltas are
+    // correct we set the location of the event to the last mouse move
+    // location.
+    event->set_location(last_mouse_position_);
+  }
+
   ForwardMouseEventToParent(event);
+
   // TODO(mgiuca): Return if event->handled() returns true. This currently
   // breaks drop-down lists which means something is incorrectly setting
   // event->handled to true (http://crbug.com/577983).
@@ -1875,7 +1889,7 @@ 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 +1968,7 @@ 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 +2514,14 @@ void RenderWidgetHostViewAura::FinishImeCompositionSession() {
 }
 
 void RenderWidgetHostViewAura::ModifyEventMovementAndCoords(
-    blink::WebMouseEvent* event) {
+    blink::WebMouseEvent* event,
+    ui::MouseEvent* ui_mouse_event) {
   // 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);
+  }
 
   // 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