add new copyTo version to SkBitmap, which takes SkColorType

BUG=skia:
R=scroggo@google.com, halcanary@google.com, bsalomon@google.com

Author: reed@google.com

Review URL: https://codereview.chromium.org/171723007

git-svn-id: http://skia.googlecode.com/svn/trunk@13553 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/utils/SkBitmapHasher.cpp b/src/utils/SkBitmapHasher.cpp
index 9f0affd..6c861cd 100644
--- a/src/utils/SkBitmapHasher.cpp
+++ b/src/utils/SkBitmapHasher.cpp
@@ -57,7 +57,7 @@
     // Hmm, that didn't work. Maybe if we create a new
     // kARGB_8888_Config version of the bitmap it will work better?
     SkBitmap copyBitmap;
-    if (!bitmap.copyTo(&copyBitmap, SkBitmap::kARGB_8888_Config)) {
+    if (!bitmap.copyTo(&copyBitmap, kPMColor_SkColorType)) {
         return false;
     }
     return ComputeDigestInternal(copyBitmap, result);