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

include/gpu/GrDrawContext.h

Index: include/gpu/GrDrawContext.h
diff --git a/include/gpu/GrDrawContext.h b/include/gpu/GrDrawContext.h
index 1a7580ea03947db7fb84de27f06545f1fe12fbb2..9e71165fed0b1e1e45ca49da8ce90d5c92113d04 100644
--- a/include/gpu/GrDrawContext.h
+++ b/include/gpu/GrDrawContext.h
@@ -264,8 +264,8 @@ public:
     }
 
     const GrSurfaceDesc& desc() const { return fRenderTarget->desc(); }
-    int width() const { return fRenderTarget->width(); }
-    int height() const { return fRenderTarget->height(); }
+    int width() const { return fWidth; }
+    int height() const { return fHeight; }
     GrPixelConfig config() const { return fRenderTarget->config(); }
     int numColorSamples() const { return fRenderTarget->numColorSamples(); }
     bool isGammaCorrect() const { return fSurfaceProps.isGammaCorrect(); }
@@ -286,7 +286,7 @@ public:
     GrAuditTrail* auditTrail() { return fAuditTrail; }
 
 protected:
-    GrDrawContext(GrContext*, GrDrawingManager*, sk_sp<GrRenderTarget>,
+    GrDrawContext(GrContext*, GrDrawingManager*, int width, int height, sk_sp<GrRenderTarget>,
                   const SkSurfaceProps* surfaceProps, GrAuditTrail*, GrSingleOwner*);
 
     GrDrawingManager* drawingManager() { return fDrawingManager; }
@@ -350,6 +350,11 @@ private:
     GrDrawTarget* getDrawTarget();
 
     GrDrawingManager*                 fDrawingManager;
+
+    // The width & height of the drawContext may be less than the width & height of the 
+    // underlying renderTarget
+    int                               fWidth;
+    int                               fHeight;
     sk_sp<GrRenderTarget>             fRenderTarget;
 
     // In MDB-mode the drawTarget can be closed by some other drawContext that has picked