Don't include headers from the layout API from other headers needlessly.

third_party/WebKit/Source/web/tests/RootScrollerTest.cpp

 // 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 "core/frame/FrameHost.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/TopControls.h"
 #include "core/html/HTMLFrameOwnerElement.h"
+#include "core/layout/LayoutBox.h"
 #include "core/page/Page.h"
 #include "core/page/scrolling/RootScrollerController.h"
 #include "core/paint/PaintLayerScrollableArea.h"
 #include "platform/testing/URLTestHelpers.h"
 #include "platform/testing/UnitTestHelpers.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebURLLoaderMockFactory.h"
 #include "public/web/WebCache.h"
 #include "public/web/WebConsoleMessage.h"
 #include "public/web/WebRemoteFrame.h"
@@ skipping 733 matching lines @@
         // EXPECT_EQ(200, container->scrollTop());
     }
 
     // Reset explicitly to prevent lifetime issues with the RemoteFrameClient.
     m_helper.reset();
 }
 
 } // namespace
 
 } // namespace blink