Make copySurface work for texture dsts, return a bool, & add unit test.

src/gpu/batches/GrCopySurfaceBatch.h

Index: src/gpu/batches/GrCopySurfaceBatch.h
diff --git a/src/gpu/batches/GrCopySurfaceBatch.h b/src/gpu/batches/GrCopySurfaceBatch.h
index 7bf8d8d8c271645a21dfcd16a50f898a687f55c5..3926643f8aedff441e2c36aece565a267c3d9ba8 100644
--- a/src/gpu/batches/GrCopySurfaceBatch.h
+++ b/src/gpu/batches/GrCopySurfaceBatch.h
@@ -17,6 +17,16 @@ class GrCopySurfaceBatch final : public GrBatch {
 public:
     DEFINE_BATCH_CLASS_ID
 
+    /** This should not really be exposed as Create() will apply this clipping, but there is
+     *  currently a workaround in GrContext::copySurface() for non-render target dsts that relies
+     *  on it. */
+    static bool ClipSrcRectAndDstPoint(const GrSurface* dst,
+                                       const GrSurface* src,
+                                       const SkIRect& srcRect,
+                                       const SkIPoint& dstPoint,
+                                       SkIRect* clippedSrcRect,
+                                       SkIPoint* clippedDstPoint);
+
     static GrBatch* Create(GrSurface* dst, GrSurface* src, const SkIRect& srcRect,
                            const SkIPoint& dstPoint);