cc: Expose clear and swap on Region

cc/occlusion_tracker.cc

 // Copyright 2012 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 "config.h"
 
 #include "cc/occlusion_tracker.h"
 
 #include <algorithm>
 
@@ skipping 93 matching lines @@
 {
     // Make sure we know about the target surface.
     enterRenderTarget(finishedTarget);
 
     RenderSurfaceType* surface = finishedTarget->renderSurface();
 
     // If the occlusion within the surface can not be applied to things outside of the surface's subtree, then clear the occlusion here so it won't be used.
     // TODO(senorblanco):  Make this smarter for SkImageFilter case:  once
     // SkImageFilters can report affectsOpacity(), call that.
     if (finishedTarget->maskLayer() || !surfaceOpacityKnown(surface) || surface->drawOpacity() < 1 || finishedTarget->filters().hasFilterThatAffectsOpacity() || finishedTarget->filter()) {
-        m_stack.back().occlusionInScreen = Region();
-        m_stack.back().occlusionInTarget = Region();
+        m_stack.back().occlusionInScreen.Clear();
+        m_stack.back().occlusionInTarget.Clear();
     } else {
         if (!surfaceTransformsToTargetKnown(surface))
-            m_stack.back().occlusionInTarget = Region();
+            m_stack.back().occlusionInTarget.Clear();
         if (!surfaceTransformsToScreenKnown(surface))
-            m_stack.back().occlusionInScreen = Region();
+            m_stack.back().occlusionInScreen.Clear();
     }
 }
 
 template<typename RenderSurfaceType>
 static inline Region transformSurfaceOpaqueRegion(const RenderSurfaceType* surface, const Region& region, const WebTransformationMatrix& transform)
 {
     // Verify that rects within the |surface| will remain rects in its target surface after applying |transform|. If this is true, then
     // apply |transform| to each rect within |region| in order to transform the entire Region.
 
     bool clipped;
@@ skipping 327 matching lines @@
     // FIXME: we could remove this helper function, but unit tests currently override this
     //        function, and they need to be verified/adjusted before this can be removed.
     return layer->drawableContentRect();
 }
 
 // Instantiate (and export) templates here for the linker.
 template class OcclusionTrackerBase<Layer, RenderSurface>;
 template class OcclusionTrackerBase<LayerImpl, RenderSurfaceImpl>;
 
 }  // namespace cc