add peekPixels to SkCanvas and SkSurface

src/core/SkDevice.cpp

Index: src/core/SkDevice.cpp
diff --git a/src/core/SkDevice.cpp b/src/core/SkDevice.cpp
index 9ce8b6b5df2e2a002bbd7fee9d5836df557c244d..364b106dd8feb023fd8223efdf6e838809a28778 100644
--- a/src/core/SkDevice.cpp
+++ b/src/core/SkDevice.cpp
@@ -65,6 +65,12 @@ SkMetaData& SkBaseDevice::getMetaData() {
     return *fMetaData;
 }
 
+// TODO: should make this guy pure-virtual.
+SkImageInfo SkBaseDevice::imageInfo() const {
+    return SkImageInfo::Make(this->width(), this->height(),
+                             kUnknown_SkColorType, kIgnore_SkAlphaType);
+}
+
 const SkBitmap& SkBaseDevice::accessBitmap(bool changePixels) {
     const SkBitmap& bitmap = this->onAccessBitmap();
     if (changePixels) {
@@ -117,3 +123,5 @@ bool SkBaseDevice::readPixels(SkBitmap* bitmap, int x, int y,
 }
 
 SkSurface* SkBaseDevice::newSurface(const SkImageInfo&) { return NULL; }
+
+const void* SkBaseDevice::peekPixels(SkImageInfo*, size_t*) { return NULL; }