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

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/renderer_host/render_widget_host_view_aura.h"
 
 #include <set>
 #include <utility>
 
 #include "base/auto_reset.h"
@@ skipping 1801 matching lines @@
     // We don't have to communicate with an input method here.
     NativeWebKeyboardEvent webkit_event(*event);
     ForwardKeyboardEvent(webkit_event);
   }
   event->SetHandled();
 }
 
 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).
 
   if (mouse_locked_) {
     aura::client::CursorClient* cursor_client =
         aura::client::GetCursorClient(window_->GetRootWindow());
     DCHECK(!cursor_client || !cursor_client->IsCursorVisible());
 
     if (event->type() == ui::ET_MOUSEWHEEL) {
@@ skipping 35 matching lines @@
         IsFractionalScaleFactor(current_device_scale_factor_)) {
       if (event->type() == ui::ET_MOUSE_MOVED ||
           event->type() == ui::ET_MOUSE_DRAGGED) {
         if ((abs(mouse_event.x - center.x()) <= 2) &&
             (abs(mouse_event.y - center.y()) <= 2)) {
           is_move_to_center_event = true;
         }
       }
     }
 
-    ModifyEventMovementAndCoords(&mouse_event);
+    ModifyEventMovementAndCoords(&mouse_event, event);
 
     bool should_not_forward = is_move_to_center_event && synthetic_move_sent_;
     if (should_not_forward) {
       synthetic_move_sent_ = false;
     } else {
       // Check if the mouse has reached the border and needs to be centered.
       if (ShouldMoveToCenter()) {
         synthetic_move_sent_ = true;
         window_->MoveCursorTo(center);
       }
@@ skipping 58 matching lines @@
         popup_child_host_view_ && popup_child_host_view_->NeedsInputGrab();
     if (CanRendererHandleEvent(event, mouse_locked_, is_selection_popup) &&
         !(event->flags() & ui::EF_FROM_TOUCH)) {
       // Confirm existing composition text on mouse press, to make sure
       // the input caret won't be moved with an ongoing composition text.
       if (event->type() == ui::ET_MOUSE_PRESSED)
         FinishImeCompositionSession();
 
       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());
       } else {
         ProcessMouseEvent(mouse_event, *event->latency());
       }
 
       // Ensure that we get keyboard focus on mouse down as a plugin window may
       // have grabbed keyboard focus.
       if (event->type() == ui::ET_MOUSE_PRESSED)
@@ skipping 525 matching lines @@
   if (!has_composition_text_)
     return;
 
   if (!!text_input_manager_ && !!text_input_manager_->GetActiveWidget()) {
     text_input_manager_->GetActiveWidget()->ImeFinishComposingText(false);
   }
   ImeCancelComposition();
 }
 
 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
   // center so that we are not limited by clipping boundaries.
   // We do not measure movement as the delta from cursor to center because
   // we may receive more mouse movement events before our warp has taken
   // effect.
   event->movementX = event->globalX - global_mouse_position_.x();
   event->movementY = event->globalY - global_mouse_position_.y();
 
@@ skipping 523 matching lines @@
           ->GetTextSelection(focused_view)
           ->GetSelectedText(&selected_text)) {
     // Set the CLIPBOARD_TYPE_SELECTION to the ui::Clipboard.
     ui::ScopedClipboardWriter clipboard_writer(ui::CLIPBOARD_TYPE_SELECTION);
     clipboard_writer.WriteText(selected_text);
   }
 #endif  // defined(USE_X11) && !defined(OS_CHROMEOS)
 }
 
 }  // namespace content