Revert of Rename kPMColor_SkColorType to kN32_SkColorType. (https://codereview.chromium.org/227433009/)

Reason for revert:
breaking the Chrome deps roll.
http://build.chromium.org/p/chromium.linux/builders/Linux%20GN%20%28dbg%29/builds/839/steps/compile/logs/stdio

Original issue's description:
> Rename kPMColor_SkColorType to kN32_SkColorType.
>
> The new name better represents what this flag means.
>
> BUG=skia:2384
>
> Committed: http://code.google.com/p/skia/source/detail?r=14117

R=reed@google.com, scroggo@google.com
TBR=reed@google.com, scroggo@google.com
NOTREECHECKS=true
NOTRY=true
BUG=skia:2384

Author: bensong@google.com

Review URL: https://codereview.chromium.org/234243002

git-svn-id: http://skia.googlecode.com/svn/trunk@14144 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/tools/skdiff_utils.cpp b/tools/skdiff_utils.cpp
index 5ca3d80..2f05239 100644
--- a/tools/skdiff_utils.cpp
+++ b/tools/skdiff_utils.cpp
@@ -85,7 +85,7 @@
 
 bool write_bitmap(const SkString& path, const SkBitmap& bitmap) {
     SkBitmap copy;
-    bitmap.copyTo(&copy, kN32_SkColorType);
+    bitmap.copyTo(&copy, kPMColor_SkColorType);
     force_all_opaque(copy);
     return SkImageEncoder::EncodeFile(path.c_str(), copy,
                                       SkImageEncoder::kPNG_Type, 100);