Move some of the adding stencil attachment logic of Gpu and into Render Target.

src/gpu/GrResourceProvider.h

Index: src/gpu/GrResourceProvider.h
diff --git a/src/gpu/GrResourceProvider.h b/src/gpu/GrResourceProvider.h
index 72efab1cefec6c1f191983daf99d8ca23177f59a..33a9f3bd1240be6e3ae90830f4932f2448511ae6 100644
--- a/src/gpu/GrResourceProvider.h
+++ b/src/gpu/GrResourceProvider.h
@@ -16,6 +16,8 @@
 class GrBatchAtlas;
 class GrIndexBuffer;
 class GrPath;
+class GrRenderTarget;
+class GrStencilAttachment;
 class GrStrokeInfo;
 class GrVertexBuffer;
 class SkDescriptor;
@@ -134,6 +136,12 @@ public:
     GrBatchAtlas* createAtlas(GrPixelConfig, int width, int height, int numPlotsX, int numPlotsY,
                               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);
+
 private:
     const GrIndexBuffer* createInstancedIndexBuffer(const uint16_t* pattern,
                                                     int patternSize,