Implement top controls show/hide functionality for main thread scrolling

public/platform/WebTopControlsState.h

 /*
  * Copyright (C) 2015 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 10 matching lines @@
  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef WebImageGenerator_h
-#define WebImageGenerator_h
-
-#include "WebCommon.h"
-
-class SkData;
-class SkImageGenerator;
+#ifndef WebTopControlsState_h
+#define WebTopControlsState_h
 
 namespace blink {
 
-class BLINK_EXPORT WebImageGenerator {
-public:
-    static SkImageGenerator* create(SkData*);
+// Represents Top Controls State. Values should be equivalent to
+// Chromium and CC versions namely: |content::TopControlsState|, and
+// |cc::TopControlsState|
+enum WebTopControlsState {
+    WebTopControlsShown = 1,
+    WebTopControlsHidden = 2,
+    WebTopControlsBoth = 3
 };
 
 } // namespace blink
-
 #endif