remove unused cachedBitmap from ImageBufferSurface

Source/platform/graphics/ImageBufferSurface.cpp

Index: Source/platform/graphics/ImageBufferSurface.cpp
diff --git a/Source/platform/graphics/ImageBufferSurface.cpp b/Source/platform/graphics/ImageBufferSurface.cpp
index 7eebf948ed7c1204aa075fffb40ecd7b452825e0..cb1ba454e7efaae984a161bb88e31166c798454e 100644
--- a/Source/platform/graphics/ImageBufferSurface.cpp
+++ b/Source/platform/graphics/ImageBufferSurface.cpp
@@ -76,21 +76,9 @@ const SkBitmap& ImageBufferSurface::bitmap()
     return canvas()->getDevice()->accessBitmap(false);
 }
 
-const SkBitmap& ImageBufferSurface::cachedBitmap() const
-{
-    DEFINE_STATIC_LOCAL(SkBitmap, nullBitmap, ());
-    return nullBitmap;
-}
-
 void ImageBufferSurface::draw(GraphicsContext* context, const FloatRect& destRect, const FloatRect& srcRect, SkXfermode::Mode op)
 {
     SkBitmap bmp = bitmap();
-    // For ImageBufferSurface that enables cachedBitmap, Use the cached bitmap for CPU side usage
-    // if it is available, otherwise generate and use it.
-    if (isAccelerated() && cachedBitmapEnabled() && isValid()) {
-        updateCachedBitmapIfNeeded();
-        bmp = cachedBitmap();
-    }
 
     RefPtr<Image> image = BitmapImage::create(bmp);