aura: No shadow for transparent window.

ash/wm/shadow_controller.cc

Index: ash/wm/shadow_controller.cc
diff --git a/ash/wm/shadow_controller.cc b/ash/wm/shadow_controller.cc
index 6f5a530ee7b9c73f5d78d70fb57ec02d1104dc6d..8575bbde9a8ac3e29a63a85ee70984d9b0355154 100644
--- a/ash/wm/shadow_controller.cc
+++ b/ash/wm/shadow_controller.cc
@@ -22,7 +22,11 @@ namespace internal {
 
 namespace {
 
-ShadowType GetShadowTypeFromWindowType(aura::Window* window) {
+ShadowType GetShadowTypeFromWindow(aura::Window* window) {
+  // No shadow for transparent window.
+  if (window->transparent())
+    return SHADOW_TYPE_NONE;
+
   switch (window->type()) {
     case aura::client::WINDOW_TYPE_NORMAL:
     case aura::client::WINDOW_TYPE_PANEL:
@@ -54,7 +58,7 @@ ShadowController::~ShadowController() {
 
 void ShadowController::OnWindowInitialized(aura::Window* window) {
   window->AddObserver(this);
-  SetShadowType(window, GetShadowTypeFromWindowType(window));
+  SetShadowType(window, GetShadowTypeFromWindow(window));
   HandlePossibleShadowVisibilityChange(window);
 }