Add ability to extract YUV planes from SkImage

include/core/SkImage.h

Index: include/core/SkImage.h
diff --git a/include/core/SkImage.h b/include/core/SkImage.h
index 62a9e9cf426bc132ded0e4fad45aa76306361b0f..32f533e4b2bdf32d9ba0b52a918ef805e9469b58 100644
--- a/include/core/SkImage.h
+++ b/include/core/SkImage.h
@@ -154,6 +154,9 @@ public:
     uint32_t uniqueID() const { return fUniqueID; }
     virtual bool isOpaque() const { return false; }
 
+    bool asYUV8Planes(const SkISize[3], void* const planes[3], const size_t rowBytes[3],

[bsalomon, 2016/01/26 16:23:48]

One thing I wondered is whether this should take a SkFilterQuality for scaling
the planes. Currently I use bilerp which should be OK for the common case of a
scale factor of 2. Our reverse conversions don't take a quality so maybe
assuming bilerp is alright.

+                      SkYUVColorSpace);
+
     virtual SkShader* newShader(SkShader::TileMode,
                                 SkShader::TileMode,
                                 const SkMatrix* localMatrix = NULL) const;