flag to use const& instead of const* for src-rect

BUG=skia:

Review URL: https://codereview.chromium.org/1272713005
diff --git a/tests/SurfaceTest.cpp b/tests/SurfaceTest.cpp
index 157ccf6..fac283d 100644
--- a/tests/SurfaceTest.cpp
+++ b/tests/SurfaceTest.cpp
@@ -705,7 +705,7 @@
     EXPECT_COPY_ON_WRITE(drawRRect(testRRect, testPaint))
     EXPECT_COPY_ON_WRITE(drawPath(testPath, testPaint))
     EXPECT_COPY_ON_WRITE(drawBitmap(testBitmap, 0, 0))
-    EXPECT_COPY_ON_WRITE(drawBitmapRect(testBitmap, testRect))
+    EXPECT_COPY_ON_WRITE(drawBitmapRect(testBitmap, testRect, nullptr))
     EXPECT_COPY_ON_WRITE(drawBitmapNine(testBitmap, testIRect, testRect, NULL))
     EXPECT_COPY_ON_WRITE(drawSprite(testBitmap, 0, 0, NULL))
     EXPECT_COPY_ON_WRITE(drawText(testText.c_str(), testText.size(), 0, 1, testPaint))