add peekPixels to SkCanvas and SkSurface

tests/SkpSkGrTest.cpp

 #if !SK_SUPPORT_GPU
 #error "GPU support required"
 #endif
 
 #include "GrContext.h"
 #include "GrContextFactory.h"
 #include "GrRenderTarget.h"
 #include "SkGpuDevice.h"
 #include "gl/GrGLDefines.h"
 
@@ skipping 435 matching lines @@
         desc.fSampleCnt = 0;
         SkAutoTUnref<GrTexture> texture(context->createUncachedTexture(desc, NULL, 0));
         if (!texture) {
             SkDebugf("unable to allocate texture for %s (w=%d h=%d)\n", fFilename,
                 dim.fX, dim.fY);
             goto finish;
         }
         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);
             int grTime = timePict(pic, &grCanvas);
             fTime = skTime - grTime;
         } else if (fTestStep == kEncodeFiles) {
             SkString pngStr = make_png_name(fFilename);
             const char* pngName = pngStr.c_str();
             writePict(grBitmap, outGrDir, pngName);
             writePict(bitmap, outSkDir, pngName);
@@ skipping 275 matching lines @@
     int testIndex = 166;
     int dirIndex = skipOverSkGr[testIndex - 166].directory;
     SkString pictDir = make_in_dir_name(dirIndex);
     if (pictDir.size() == 0) {
         return;
     }
     SkString filename(skipOverSkGr[testIndex - 166].filename);
     TestResult::Test(dirIndex, filename.c_str(), kCompareBits, reporter->verbose());
     TestResult::Test(dirIndex, filename.c_str(), kEncodeFiles, reporter->verbose());
 }