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/tests/BitmapHasherTest.cpp b/tests/BitmapHasherTest.cpp
index 924cea2..d6c9e6a 100644
--- a/tests/BitmapHasherTest.cpp
+++ b/tests/BitmapHasherTest.cpp
@@ -31,7 +31,7 @@
                               SkColor color) {
             bitmap.setConfig(config, width, height);
             REPORTER_ASSERT(fReporter, bitmap.allocPixels());
-            bitmap.setIsOpaque(true);
+            bitmap.setAlphaType(kOpaque_SkAlphaType);
             bitmap.eraseColor(color);
         }