SkImage method for detecting lazy decoding

BUG=skia:4224
R=reed@google.com

Review URL: https://codereview.chromium.org/1305453007
diff --git a/src/image/SkImage_Raster.cpp b/src/image/SkImage_Raster.cpp
index 120c397..51bc6f0 100644
--- a/src/image/SkImage_Raster.cpp
+++ b/src/image/SkImage_Raster.cpp
@@ -93,6 +93,10 @@
         SkASSERT(fBitmap.isImmutable());
     }
 
+    bool onIsLazyGenerated() const override {
+        return fBitmap.pixelRef() && fBitmap.pixelRef()->isLazyGenerated();
+    }
+
 private:
     SkImage_Raster() : INHERITED(0, 0, kNeedNewImageUniqueID, NULL) {
         fBitmap.setImmutable();