Convert MouseEvents from DIPS to Pixels before passing it to surfaces for hittesting.

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 bbb79c967405304c7bb46b1823dfea04d09bf7f0..35a8f9d6d4e726ddad1febfaaae05bb4e5a39c73 100644
--- a/content/browser/renderer_host/render_widget_host_view_aura.cc
+++ b/content/browser/renderer_host/render_widget_host_view_aura.cc
@@ -80,6 +80,7 @@
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/color_profile.h"
 #include "ui/gfx/display.h"
+#include "ui/gfx/geometry/dip_util.h"
 #include "ui/gfx/geometry/rect_conversions.h"
 #include "ui/gfx/geometry/size_conversions.h"
 #include "ui/gfx/screen.h"
@@ -502,6 +503,10 @@ RenderWidgetHostViewAura::RenderWidgetHostViewAura(RenderWidgetHost* host,
   selection_controller_client_.reset(
       new TouchSelectionControllerClientAura(this));
   CreateSelectionController();
+
+  const gfx::Display display =
+      gfx::Screen::GetScreenFor(window_)->GetDisplayNearestWindow(window_);
+  device_scale_factor_ = display.device_scale_factor();

[sadrul, 2015/11/03 18:00:00]

Note that at this point, |window_| hasn't been attached to a window-tree yet. So
GetDisplayNearestWindow() wouldn't necessarily give the right result. The better
place for this would be in the three InitAs* methods, where |window_| is
attached. In InitAsChild(), you should get the Display nearest |parent_view|. In
InitAsPopup() and InitAsFullscreen(), you should get the Display nearest
|window_| after the calls to ParentWindowWithContext(). That way, you start with
the correct DSF. In the ctor initialize-list, you should initialize
|device_scale_factor_| to some default value

[lfg, 2015/11/03 20:49:15]

Done. I've also added a DCHECK to make sure it's initialized before we use it.

 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -1883,6 +1888,7 @@ void RenderWidgetHostViewAura::OnDeviceScaleFactorChanged(
 
   UpdateScreenInfo(window_);
 
+  device_scale_factor_ = device_scale_factor;
   const gfx::Display display = gfx::Screen::GetScreenFor(window_)->
       GetDisplayNearestWindow(window_);
   DCHECK_EQ(device_scale_factor, display.device_scale_factor());
@@ -2174,8 +2180,13 @@ void RenderWidgetHostViewAura::OnMouseEvent(ui::MouseEvent* event) {
 uint32_t RenderWidgetHostViewAura::SurfaceIdNamespaceAtPoint(
     const gfx::Point& point,
     gfx::Point* transformed_point) {
-  cc::SurfaceId id =
-      delegated_frame_host_->SurfaceIdAtPoint(point, transformed_point);
+  gfx::Point point_in_pixels =
+      gfx::ConvertPointToPixel(device_scale_factor_, point);
+  cc::SurfaceId id = delegated_frame_host_->SurfaceIdAtPoint(point_in_pixels,
+                                                             transformed_point);
+  *transformed_point =
+      gfx::ConvertPointToDIP(device_scale_factor_, *transformed_point);

[sadrul, 2015/11/03 18:00:00]

Add a comment here to clarify that surface-hittest happens in device-pixels.

[lfg, 2015/11/03 20:49:16]

Done.

+
   // It is possible that the renderer has not yet produced a surface, in which
   // case we return our current namespace.
   if (id.is_null())