Free temporary GPU and memory resources held by inactive or hidden 2D canvases

Source/platform/graphics/ImageBuffer.h

Index: Source/platform/graphics/ImageBuffer.h
diff --git a/Source/platform/graphics/ImageBuffer.h b/Source/platform/graphics/ImageBuffer.h
index 25831223c3f19aa4df096ef0664b25e3c9c0c57b..9ad83a16023416a7c97d43a853579f5348877860 100644
--- a/Source/platform/graphics/ImageBuffer.h
+++ b/Source/platform/graphics/ImageBuffer.h
@@ -81,6 +81,8 @@ public:
     const IntSize& size() const { return m_surface->size(); }
     bool isAccelerated() const { return m_surface->isAccelerated(); }
 
+    void setIsHidden(bool hidden) { m_surface->setIsHidden(hidden); }
+
     GraphicsContext* context() const;
 
     const SkBitmap& bitmap() const;