add peekPixels to canvas

src/core/SkCanvas.cpp

Index: src/core/SkCanvas.cpp
diff --git a/src/core/SkCanvas.cpp b/src/core/SkCanvas.cpp
index ed8274dc5d3b4a9bf09d6241541620b1a11f9a4f..bcfc79e656ace741873beabaacbe5b3409e41eb2 100644
--- a/src/core/SkCanvas.cpp
+++ b/src/core/SkCanvas.cpp
@@ -992,6 +992,15 @@ SkSurface* SkCanvas::onNewSurface(const SkImageInfo& info) {
     return dev ? dev->newSurface(info) : NULL;
 }
 
+const void* SkCanvas::peekPixels(SkImageInfo* info, size_t* rowBytes) {
+    return this->onPeekPixels(info, rowBytes);
+}
+
+const void* SkCanvas::onPeekPixels(SkImageInfo* info, size_t* rowBytes) {
+    SkBaseDevice* dev = this->getDevice();
+    return dev ? dev->peekPixels(info, rowBytes) : NULL;
+}
+
 /////////////////////////////////////////////////////////////////////////////
 
 void SkCanvas::internalDrawBitmap(const SkBitmap& bitmap,