Make compositor and blink talk in fractional scroll offset

public/platform/WebDoublePoint.h

 /*
  * Copyright 2014 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 13 matching lines @@
  * 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 WebDoublePoint_h
 #define WebDoublePoint_h
 
+#include "WebCommon.h"
+
+#if INSIDE_BLINK
+#include "platform/geometry/DoublePoint.h"
+#endif
+
 namespace blink {
 
 struct WebDoublePoint {
     double x;
     double y;
 
     WebDoublePoint()
         : x(0.0)
         , y(0.0)
     {
     }
 
     WebDoublePoint(double x, double y)
         : x(x)
         , y(y)
     {
     }
+
+#if INSIDE_BLINK
+    WebDoublePoint(const DoublePoint& p)
+        : x(p.x())
+        , y(p.y())
+    {
+    }
+
+    operator DoublePoint() const
+    {
+        return DoublePoint(x, y);
+    }
+#endif
+
 };
 
 inline bool operator==(const WebDoublePoint& a, const WebDoublePoint& b)
 {
     return a.x == b.x && a.y == b.y;
 }
 
 inline bool operator!=(const WebDoublePoint& a, const WebDoublePoint& b)
 {
     return !(a == b);
 }
 
 } // namespace blink
 
 #endif