detect when we can filter bitmaps/images directly, w/o a tmp layer

src/image/SkImage_Gpu.cpp

Index: src/image/SkImage_Gpu.cpp
diff --git a/src/image/SkImage_Gpu.cpp b/src/image/SkImage_Gpu.cpp
index 346f7983b71eff2838ebf132c44111554fd24048..55a82bba8701b86e059fd7283f73941bf55d4911 100644
--- a/src/image/SkImage_Gpu.cpp
+++ b/src/image/SkImage_Gpu.cpp
@@ -5,16 +5,18 @@
  * found in the LICENSE file.
  */
 
-#include "SkBitmapCache.h"
-#include "SkImage_Gpu.h"
 #include "GrCaps.h"
 #include "GrContext.h"
 #include "GrDrawContext.h"
 #include "GrTextureParamsAdjuster.h"
 #include "effects/GrYUVtoRGBEffect.h"
 #include "SkCanvas.h"
+#include "SkBitmapCache.h"
 #include "SkGpuDevice.h"
+#include "SkGrPixelRef.h"
 #include "SkGrPriv.h"
+#include "SkImageFilter.h"
+#include "SkImage_Gpu.h"
 #include "SkPixelRef.h"
 
 SkImage_Gpu::SkImage_Gpu(int w, int h, uint32_t uniqueID, SkAlphaType at, GrTexture* tex,
@@ -69,6 +71,13 @@ bool SkImage_Gpu::getROPixels(SkBitmap* dst, CachingHint chint) const {
     return true;
 }
 
+bool SkImage_Gpu::asBitmapForImageFilters(SkBitmap* bitmap) const {
+    bitmap->setInfo(make_info(this->width(), this->height(), this->isOpaque()));
+    bitmap->setPixelRef(new SkGrPixelRef(bitmap->info(), fTexture))->unref();
+    bitmap->pixelRef()->setImmutableWithID(this->uniqueID());
+    return true;
+}
+
 class GpuImage_GrTextureAdjuster : public GrTextureAdjuster {
 public:
     GpuImage_GrTextureAdjuster(const SkImage_Gpu* image)
@@ -166,9 +175,6 @@ SkImage* SkImage_Gpu::onNewSubset(const SkIRect& subset) const {
 
 ///////////////////////////////////////////////////////////////////////////////////////////////////
 
-#include "SkGrPixelRef.h"
-#include "SkImageFilter.h"
-
 class SkGpuImageFilterProxy : public SkImageFilter::Proxy {
     GrContext* fCtx;