app_list: Fix shadow bleeds over launcher button and steals mouse events

ui/aura/window.cc

Index: ui/aura/window.cc
diff --git a/ui/aura/window.cc b/ui/aura/window.cc
index 1c2554723ede63c285812daa116b96f431580285..62b77883901df9aad1e7eb11921b4e0d8d663753 100644
--- a/ui/aura/window.cc
+++ b/ui/aura/window.cc
@@ -29,6 +29,7 @@
 #include "ui/compositor/compositor.h"
 #include "ui/compositor/layer.h"
 #include "ui/gfx/canvas.h"
+#include "ui/gfx/path.h"
 #include "ui/gfx/screen.h"
 
 namespace aura {
@@ -442,8 +443,19 @@ bool Window::HitTest(const gfx::Point& local_point) {
   // probably cheaper to do the math every time than to branch).
   gfx::Rect local_bounds(gfx::Point(), bounds().size());
   local_bounds.Inset(hit_test_bounds_override_outer_);
-  // TODO(beng): hittest masks.
-  return local_bounds.Contains(local_point);
+
+  if (!delegate_ || !delegate_->HasHitTestMask())
+    return local_bounds.Contains(local_point);
+
+  gfx::Path mask;
+  delegate_->GetHitTestMask(&mask);
+
+  SkRegion clip_region;
+  clip_region.setRect(local_bounds.x(), local_bounds.y(),
+                      local_bounds.width(), local_bounds.height());
+  SkRegion mask_region;
+  return mask_region.setPath(mask, clip_region) &&
+      mask_region.contains(local_point.x(), local_point.y());
 }
 
 Window* Window::GetEventHandlerForPoint(const gfx::Point& local_point) {