scaling API on SkPixmap

BUG=skia:4481

Review URL: https://codereview.chromium.org/1463373002
diff --git a/src/core/SkBitmapController.cpp b/src/core/SkBitmapController.cpp
index 5cfa525..233e811 100644
--- a/src/core/SkBitmapController.cpp
+++ b/src/core/SkBitmapController.cpp
@@ -121,8 +121,10 @@
         
         SkASSERT(fResultBitmap.getPixels());
         fResultBitmap.setImmutable();
-        if (SkBitmapCache::AddWH(desc, fResultBitmap)) {
-            provider.notifyAddedToCache();
+        if (!provider.isVolatile()) {
+            if (SkBitmapCache::AddWH(desc, fResultBitmap)) {
+                provider.notifyAddedToCache();
+            }
         }
     }