Add wrapBackendTextureAsRenderTarget API

src/gpu/GrResourceProvider.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrResourceProvider_DEFINED
 #define GrResourceProvider_DEFINED
 
@@ skipping 129 matching lines @@
                               GrBatchAtlas::EvictionFunc func, void* data);
 
     /**
      * If passed in render target already has a stencil buffer, return it. Otherwise attempt to
      * attach one.
      */
     GrStencilAttachment* attachStencilAttachment(GrRenderTarget* rt);
 
     const GrCaps* caps() { return this->gpu()->caps(); }
 
+     /**
+      * 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,
+                                                      GrWrapOwnership = kBorrow_GrWrapOwnership);
+
 private:
     const GrIndexBuffer* createInstancedIndexBuffer(const uint16_t* pattern,
                                                     int patternSize,
                                                     int reps,
                                                     int vertCount,
                                                     const GrUniqueKey& key);
 
     const GrIndexBuffer* createQuadIndexBuffer();
 
     GrUniqueKey fQuadIndexBufferKey;
 
     typedef GrTextureProvider INHERITED;
 };
 
 #endif