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/ports/SkImageDecoder_CG.cpp b/src/ports/SkImageDecoder_CG.cpp
index 90c282d..c61ce98 100644
--- a/src/ports/SkImageDecoder_CG.cpp
+++ b/src/ports/SkImageDecoder_CG.cpp
@@ -208,8 +208,8 @@
             // format.
             // <Error>: CGImageDestinationFinalize image destination does not have enough images
             // So instead we copy to 8888.
-            if (bm.config() == SkBitmap::kARGB_4444_Config) {
-                bm.copyTo(&bitmap8888, SkBitmap::kARGB_8888_Config);
+            if (bm.colorType() == kARGB_4444_SkColorType) {
+                bm.copyTo(&bitmap8888, kPMColor_SkColorType);
                 bmPtr = &bitmap8888;
             }
             type = kUTTypePNG;