fix undefined signed shifts

include/core/SkCanvas.h

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkCanvas_DEFINED
 #define SkCanvas_DEFINED
 
@@ skipping 36 matching lines @@
     the clips in the stack.
 
     While the Canvas holds the state of the drawing device, the state (style)
     of the object being drawn is held by the Paint, which is provided as a
     parameter to each of the draw() methods. The Paint holds attributes such as
     color, typeface, textSize, strokeWidth, shader (e.g. gradients, patterns),
     etc.
 */
 class SK_API SkCanvas : public SkRefCnt {
     enum PrivateSaveLayerFlags {
-        kDontClipToLayer_PrivateSaveLayerFlag   = 1 << 31,
+        kDontClipToLayer_PrivateSaveLayerFlag   = 1U << 31,
     };
     
 public:
     /**
      *  Attempt to allocate raster canvas, matching the ImageInfo, that will draw directly into the
      *  specified pixels. To access the pixels after drawing to them, the caller should call
      *  flush() or call peekPixels(...).
      *
      *  On failure, return NULL. This can fail for several reasons:
      *  1. invalid ImageInfo (e.g. negative dimensions)
@@ skipping 1427 matching lines @@
 
 class SkCanvasClipVisitor {
 public:
     virtual ~SkCanvasClipVisitor();
     virtual void clipRect(const SkRect&, SkRegion::Op, bool antialias) = 0;
     virtual void clipRRect(const SkRRect&, SkRegion::Op, bool antialias) = 0;
     virtual void clipPath(const SkPath&, SkRegion::Op, bool antialias) = 0;
 };
 
 #endif