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],

[reed1, 2016/01/26 16:06:45]

Is this intended to always succeed, even if the underlying form is not
intrinsically YUV? (e.g. rgb or picture)

Matt and Leon have gone to great lengths to allow the codec to specify the
sizes/rowbytes for each plane (including padding sometimes). How does the caller
arrive at the specified sizes here?

[bsalomon, 2016/01/26 16:32:50]

Yes, it is for turning a SkImage into a video frame. The motivating use case is
for taking rendered canvas2D frames and turning them into a video stream. So
typically the content behind the image is a newImageSnapshot ()from a GPU
(though probably could be CPU) SkSurface. I hadn't thought about cases where the
original data is YUV. That would accelerate that use but isn't really the target
use case.
That would based on what the video encoder can ingest, probably 4:2:0 (y full
sized, u and v half sized in both dimensions).

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