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

content/browser/renderer_host/render_widget_host_view_mac.mm

Index: content/browser/renderer_host/render_widget_host_view_mac.mm
diff --git a/content/browser/renderer_host/render_widget_host_view_mac.mm b/content/browser/renderer_host/render_widget_host_view_mac.mm
index fb8951657c224d84ff28b942dad3ade8ec639b68..f8c2a2ab6a55c98aec4590f5c5769f514eb03aa2 100644
--- a/content/browser/renderer_host/render_widget_host_view_mac.mm
+++ b/content/browser/renderer_host/render_widget_host_view_mac.mm
@@ -1593,8 +1593,16 @@ uint32_t RenderWidgetHostViewMac::GetSurfaceIdNamespace() {
 uint32_t RenderWidgetHostViewMac::SurfaceIdNamespaceAtPoint(
     const gfx::Point& point,
     gfx::Point* transformed_point) {
-  cc::SurfaceId id =
-      delegated_frame_host_->SurfaceIdAtPoint(point, transformed_point);
+  // The surface hittest happens in device pixels, so we need to convert the
+  // |point| from DIPs to pixels before hittesting.
+  float scale_factor = gfx::Screen::GetScreenFor(cocoa_view_)
+                           ->GetDisplayNearestWindow(cocoa_view_)
+                           .device_scale_factor();

[Avi (use Gerrit), 2015/11/04 20:16:47]

I'm thinking in Cocoa, and would instinctively do

float scale_factor = [[cocoa_view_ window] backingScaleFactor];

asking the window itself what the scale factor was, rather than wandering around
like this. I guess this is the fancy gfx:: way we do it? (shrug)

+  gfx::Point point_in_pixels = gfx::ConvertPointToPixel(scale_factor, point);
+  cc::SurfaceId id = delegated_frame_host_->SurfaceIdAtPoint(point_in_pixels,
+                                                             transformed_point);
+  *transformed_point = gfx::ConvertPointToDIP(scale_factor, *transformed_point);
+
   // It is possible that the renderer has not yet produced a surface, in which
   // case we return our current namespace.
   if (id.is_null())