add SkBitmap::installPixelRef()

src/core/SkScaledImageCache.cpp

Index: src/core/SkScaledImageCache.cpp
diff --git a/src/core/SkScaledImageCache.cpp b/src/core/SkScaledImageCache.cpp
index fc3148bdd8807a31f0660c7f45b36e78bdcd1f41..c8a793d03ef00ffaaca2c5cc91d46cc71bdb3564 100644
--- a/src/core/SkScaledImageCache.cpp
+++ b/src/core/SkScaledImageCache.cpp
@@ -293,14 +293,10 @@ bool SkScaledImageCacheDiscardableAllocator::allocPixelRef(SkBitmap* bitmap,
         return false;
     }
 
-    SkImageInfo info = {
-        bitmap->width(),
-        bitmap->height(),
-        kPMColor_SkColorType,
-        bitmap->alphaType()
-    };
-
-    bitmap->setPixelRef(SkNEW_ARGS(SkOneShotDiscardablePixelRef,
+    SkImageInfo info = SkImageInfo::MakePM(bitmap->width(), bitmap->height(),
+                                           bitmap->alphaType());
+
+    bitmap->installPixelRef(SkNEW_ARGS(SkOneShotDiscardablePixelRef,
                                    (info, dm, bitmap->rowBytes())))->unref();
     bitmap->lockPixels();
     return bitmap->readyToDraw();