change asABitmap to isABitmap on shader

src/core/SkPictureShader.cpp

Index: src/core/SkPictureShader.cpp
diff --git a/src/core/SkPictureShader.cpp b/src/core/SkPictureShader.cpp
index e04e248756ea90e4d4a27ed003fbbf8f2acaa9b6..f8c2ab09f8e4c37eec252ffe56180d8bf96f6602 100644
--- a/src/core/SkPictureShader.cpp
+++ b/src/core/SkPictureShader.cpp
@@ -83,12 +83,14 @@ struct BitmapShaderRec : public SkResourceCache::Rec {
         result->reset(SkRef(rec.fShader.get()));
 
         SkBitmap tile;
-        rec.fShader.get()->asABitmap(&tile, NULL, NULL);
-        // FIXME: this doesn't protect the pixels from being discarded as soon as we unlock.
-        // Should be handled via a pixel ref generator instead
-        // (https://code.google.com/p/skia/issues/detail?id=3220).
-        SkAutoLockPixels alp(tile, true);
-        return tile.getPixels() != NULL;
+        if (rec.fShader.get()->isABitmap(&tile, NULL, NULL)) {
+            // FIXME: this doesn't protect the pixels from being discarded as soon as we unlock.
+            // Should be handled via a pixel ref generator instead
+            // (https://code.google.com/p/skia/issues/detail?id=3220).
+            SkAutoLockPixels alp(tile, true);
+            return tile.getPixels() != NULL;
+        }
+        return false;
     }
 };