Dynamically create stencil buffer when needed.

src/gpu/gl/GrGLRenderTarget.h

Index: src/gpu/gl/GrGLRenderTarget.h
diff --git a/src/gpu/gl/GrGLRenderTarget.h b/src/gpu/gl/GrGLRenderTarget.h
index 4d08c1493a3009974fad3b7bf8f7b57f5c84cc4b..7e7349257f054ac44e8a32cd5626c1cf94e1041c 100644
--- a/src/gpu/gl/GrGLRenderTarget.h
+++ b/src/gpu/gl/GrGLRenderTarget.h
@@ -54,6 +54,9 @@ public:
         }
     }
 
+    /** When we don't own the FBO ID we don't attempt to modify its attachments. */
+    bool canAttemptStencilAttachment() const SK_OVERRIDE { return !fIsWrapped; }
+
 protected:
     // The public constructor registers this object with the cache. However, only the most derived
     // class should register with the cache. This constructor does not do the registration and