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/SkImageDecoder_wbmp.cpp b/src/images/SkImageDecoder_wbmp.cpp
index 4a9944d..8dce62c 100644
--- a/src/images/SkImageDecoder_wbmp.cpp
+++ b/src/images/SkImageDecoder_wbmp.cpp
@@ -111,8 +111,8 @@
     int width = head.fWidth;
     int height = head.fHeight;
 
-    decodedBitmap->setConfig(SkBitmap::kIndex8_Config, width, height);
-    decodedBitmap->setIsOpaque(true);
+    decodedBitmap->setConfig(SkBitmap::kIndex8_Config, width, height, 0,
+                             kOpaque_SkAlphaType);
 
     if (SkImageDecoder::kDecodeBounds_Mode == mode) {
         return true;