[devtools] Allow transparent base background color overrides.

third_party/WebKit/Source/web/InspectorEmulationAgent.cpp

 // Copyright 2015 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 "web/InspectorEmulationAgent.h"
 
 #include "core/frame/FrameHost.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/Settings.h"
 #include "core/inspector/protocol/DOM.h"
@@ skipping 170 matching lines @@
 void InspectorEmulationAgent::virtualTimeBudgetExpired() {
   m_webLocalFrameImpl->view()->scheduler()->setVirtualTimePolicy(
       WebViewScheduler::VirtualTimePolicy::PAUSE);
   frontend()->virtualTimeBudgetExpired();
 }
 
 Response InspectorEmulationAgent::setDefaultBackgroundColorOverride(
     Maybe<protocol::DOM::RGBA> color) {
   if (!color.isJust()) {
     // Clear the override and state.
-    webViewImpl()->setBaseBackgroundColorOverride(Color::transparent);
+    webViewImpl()->clearBaseBackgroundColorOverride();
     m_state->remove(EmulationAgentState::defaultBackgroundColorOverrideRGBA);
     return Response::OK();
   }
 
   blink::protocol::DOM::RGBA* rgba = color.fromJust();
   m_state->setValue(EmulationAgentState::defaultBackgroundColorOverrideRGBA,
                     rgba->toValue());
   // Clamping of values is done by Color() constructor.
   int alpha = lroundf(255.0f * rgba->getA(1.0f));
   webViewImpl()->setBaseBackgroundColorOverride(
       Color(rgba->getR(), rgba->getG(), rgba->getB(), alpha).rgb());
   return Response::OK();
 }
 
 DEFINE_TRACE(InspectorEmulationAgent) {
   visitor->trace(m_webLocalFrameImpl);
   InspectorBaseAgent::trace(visitor);
 }
 
 }  // namespace blink