remove unused cachedBitmap from ImageBufferSurface

Source/platform/graphics/ImageBufferSurface.h

Index: Source/platform/graphics/ImageBufferSurface.h
diff --git a/Source/platform/graphics/ImageBufferSurface.h b/Source/platform/graphics/ImageBufferSurface.h
index c2be36514191f87e61d25b80b4ab62fa78649d5c..57c18fd96a8e07d0adc9dbcbe181de378ec2ed83 100644
--- a/Source/platform/graphics/ImageBufferSurface.h
+++ b/Source/platform/graphics/ImageBufferSurface.h
@@ -67,11 +67,7 @@ public:
     virtual bool isAccelerated() const { return false; }
     virtual bool isRecording() const { return false; }
     virtual void didModifyBackingTexture() { }
-    virtual bool cachedBitmapEnabled() const { return false; }
     virtual bool isExpensiveToPaint() { return false; }
-    virtual const SkBitmap& cachedBitmap() const;
-    virtual void invalidateCachedBitmap() { }
-    virtual void updateCachedBitmapIfNeeded() { }
     virtual void setFilterQuality(SkFilterQuality) { }
     virtual void setIsHidden(bool) { }
     virtual void setImageBuffer(ImageBuffer*) { }