Implement windows mousewheel scroll by page functionality

cc/input/input_handler.h

Index: cc/input/input_handler.h
diff --git a/cc/input/input_handler.h b/cc/input/input_handler.h
index 04973d5e06a7fe0f6a3293df9ddee7a48431ed76..7be60a1e1a9587983264ad1d4e8c6a22e6c5275e 100644
--- a/cc/input/input_handler.h
+++ b/cc/input/input_handler.h
@@ -8,6 +8,7 @@
 #include "base/basictypes.h"
 #include "base/time.h"
 #include "cc/base/cc_export.h"
+#include "third_party/WebKit/Source/Platform/chromium/public/WebScrollbar.h"
 
 namespace gfx {
 class Point;
@@ -51,6 +52,10 @@ class CC_EXPORT InputHandlerClient {
   virtual bool ScrollBy(gfx::Point viewport_point,
                         gfx::Vector2dF scroll_delta) = 0;
 
+  virtual bool ScrollVerticallyByPage(
+      gfx::Point viewport_point,
+      WebKit::WebScrollbar::ScrollDirection direction) = 0;
+
   // Stop scrolling the selected layer. Should only be called if ScrollBegin()
   // returned ScrollStarted.
   virtual void ScrollEnd() = 0;