Add desired width & height to drawContext (as opposed to using the width & height of the RT)

include/gpu/GrContext.h

Index: include/gpu/GrContext.h
diff --git a/include/gpu/GrContext.h b/include/gpu/GrContext.h
index 3a57cd8e287e89ffd4764133e0b28d5bc166ae15..077ad40a1fada49bc50b1973a40d02d4126b9966 100644
--- a/include/gpu/GrContext.h
+++ b/include/gpu/GrContext.h
@@ -184,12 +184,16 @@ public:
      * Callers assume the creation ref of the drawContext
      * NULL will be returned if the context has been abandoned.
      *
+     * @param  width        width of the portion of the rt that will actually be drawn to
+     * @param  height       height of the portion of the rt that will actually be drawn to
      * @param  rt           the render target receiving the draws
      * @param  surfaceProps the surface properties (mainly defines text drawing)
      *
      * @return a draw context
      */
-    sk_sp<GrDrawContext> drawContext(sk_sp<GrRenderTarget> rt, const SkSurfaceProps* = nullptr);
+    sk_sp<GrDrawContext> drawContext(int width, int height,
+                                     sk_sp<GrRenderTarget> rt,
+                                     const SkSurfaceProps* = nullptr);
 
     /**
      * Create both a GrRenderTarget and a matching GrDrawContext to wrap it.