store SkAlphaType inside SkBitmap, on road to support unpremul

BUG=
R=bsalomon@google.com, scroggo@google.com

Review URL: https://codereview.chromium.org/25275004

git-svn-id: http://skia.googlecode.com/svn/trunk@11877 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/images/SkImageRef.cpp b/src/images/SkImageRef.cpp
index 9093b05..ead835f 100644
--- a/src/images/SkImageRef.cpp
+++ b/src/images/SkImageRef.cpp
@@ -64,7 +64,8 @@
 bool SkImageRef::isOpaque(SkBitmap* bitmap) {
     if (bitmap && bitmap->pixelRef() == this) {
         bitmap->lockPixels();
-        bitmap->setIsOpaque(fBitmap.isOpaque());
+        // what about colortables??????
+        bitmap->setAlphaType(fBitmap.alphaType());
         bitmap->unlockPixels();
         return true;
     }