When possible, draw the toolbar shadow with the compositor

chrome/browser/android/compositor/scene_layer/toolbar_scene_layer.cc

 // Copyright 2016 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 "chrome/browser/android/compositor/scene_layer/toolbar_scene_layer.h"
 
 #include "base/android/jni_android.h"
 #include "base/android/jni_array.h"
 #include "cc/layers/solid_color_layer.h"
 #include "chrome/browser/android/compositor/layer/toolbar_layer.h"
@@ skipping 18 matching lines @@
 }
 
 ToolbarSceneLayer::~ToolbarSceneLayer() {
 }
 
 void ToolbarSceneLayer::UpdateToolbarLayer(
     JNIEnv* env,
     const JavaParamRef<jobject>& object,
     const JavaParamRef<jobject>& jresource_manager,
     jint toolbar_resource_id,
+    jint toolbar_shadow_resource_id,
     jint toolbar_background_color,
     jint url_bar_resource_id,
     jfloat url_bar_alpha,
     jfloat top_offset,
     bool visible,
     bool show_shadow) {
   // If the toolbar layer has not been created yet, create it.
   if (!toolbar_layer_) {
     ui::ResourceManager* resource_manager =
         ui::ResourceManagerImpl::FromJavaObject(jresource_manager);
     toolbar_layer_ = ToolbarLayer::Create(resource_manager);
     toolbar_layer_->layer()->SetHideLayerAndSubtree(true);
     layer_->AddChild(toolbar_layer_->layer());
   }
 
   toolbar_layer_->layer()->SetHideLayerAndSubtree(!visible);
   if (visible) {
     toolbar_layer_->layer()->SetPosition(gfx::PointF(0, top_offset));
-    // If we're at rest, hide the shadow.  The Android view should be drawing.
-    bool clip_shadow = top_offset >= 0.f && !show_shadow;
-    toolbar_layer_->PushResource(toolbar_resource_id, toolbar_background_color,
+    toolbar_layer_->PushResource(toolbar_resource_id,
+                                 toolbar_shadow_resource_id,
+                                 toolbar_background_color,
                                  false, SK_ColorWHITE, url_bar_resource_id,
-                                 url_bar_alpha, false, clip_shadow);
+                                 url_bar_alpha, false, show_shadow);
   }
 }
 
 void ToolbarSceneLayer::UpdateProgressBar(JNIEnv* env,
                                        const JavaParamRef<jobject>& object,
                                        jint progress_bar_x,
                                        jint progress_bar_y,
                                        jint progress_bar_width,
                                        jint progress_bar_height,
                                        jint progress_bar_color,
@@ skipping 49 matching lines @@
       new ToolbarSceneLayer(env, jobj);
   return reinterpret_cast<intptr_t>(toolbar_scene_layer);
 }
 
 bool RegisterToolbarSceneLayer(JNIEnv* env) {
   return RegisterNativesImpl(env);
 }
 
 }  // namespace android
 }  // namespace chrome