Add wrapBackendTextureAsRenderTarget API

include/gpu/GrTextureProvider.h

Index: include/gpu/GrTextureProvider.h
diff --git a/include/gpu/GrTextureProvider.h b/include/gpu/GrTextureProvider.h
index 338dddbaca87f0a87c89c29129afad0ae3fadac4..f943da33667c998aef69e98ac0d4ca5b09716391 100644
--- a/include/gpu/GrTextureProvider.h
+++ b/include/gpu/GrTextureProvider.h
@@ -98,10 +98,19 @@ public:
      * the client will resolve to a texture). Currently wrapped render targets
      * always use the kBorrow_GrWrapOwnership semantics.
      *
-     * @return GrTexture object or NULL on failure.
+     * @return GrRenderTarget object or NULL on failure.
      */
      GrRenderTarget* wrapBackendRenderTarget(const GrBackendRenderTargetDesc& desc);
 
+     /**
+      * Wraps an existing texture with a GrRenderTarget object. This is useful when the provided
+      * texture has a format that cannot be textured from by Skia, but we want to raster to it.
+      *
+      * @return GrRenderTarget object or NULL on failure.
+      */
+     GrRenderTarget* wrapBackendTextureAsRenderTarget(const GrBackendTextureDesc& desc,

[bsalomon, 2016/02/22 16:41:01]

Can we put this in GrResourceProvider (it's a derived private class of
TexturProvider)? I'd eventually like to hide wrapBackendRT and
wrapBackendTexture there as well and only expose these imports of foreign
textures through SkSurface and SkImage.

[ericrk, 2016/02/22 21:02:59]

I was planning on calling this directly from Chrome. I'm happy to use an
SkSurface/SkImage wrapper, but I think we currently need to get a GrSurface (not
an SkSurface) so we can call prepareForExternalIO on it... happy to re-work this
though. WDYT?

[bsalomon, 2016/02/23 02:25:27]

Gotcha, what if we added a prepareForExternalIO (or similar) to SkSurface?

[ericrk, 2016/02/24 00:39:53]

Added this function.

+                                                      GrWrapOwnership = kBorrow_GrWrapOwnership);
+
 protected:
     GrTextureProvider(GrGpu* gpu, GrResourceCache* cache, GrSingleOwner* singleOwner);