add peekPixels to SkCanvas and SkSurface

tests/SkpSkGrTest.cpp

Index: tests/SkpSkGrTest.cpp
diff --git a/tests/SkpSkGrTest.cpp b/tests/SkpSkGrTest.cpp
index 02aabbe2af0258aa41d885f9ad45d5e84aeb2de6..d1d38dfe8e2702b3e0e3dd01fc09088c5bd5e269 100644
--- a/tests/SkpSkGrTest.cpp
+++ b/tests/SkpSkGrTest.cpp
@@ -453,7 +453,11 @@ void TestResult::testOne() {
         SkGpuDevice grDevice(context, texture.get());
         SkCanvas grCanvas(&grDevice);
         drawPict(pic, &grCanvas, fScaleOversized ? scale : 1);
-        const SkBitmap& grBitmap = grDevice.accessBitmap(false);
+
+        SkBitmap grBitmap;
+        grBitmap.allocPixels(grCanvas.imageInfo());
+        grCanvas.readPixels(&grBitmap, 0, 0);
+        
         if (fTestStep == kCompareBits) {
             fPixelError = similarBits(grBitmap, bitmap);
             int skTime = timePict(pic, &skCanvas);