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/skpdiff/SkDiffContext.cpp b/tools/skpdiff/SkDiffContext.cpp
index 6f0b09f..b9c55c1 100644
--- a/tools/skpdiff/SkDiffContext.cpp
+++ b/tools/skpdiff/SkDiffContext.cpp
@@ -122,7 +122,7 @@
 
             // compute the image diff and output it
             SkBitmap copy;
-            diffData.fResult.poiAlphaMask.copyTo(&copy, kN32_SkColorType);
+            diffData.fResult.poiAlphaMask.copyTo(&copy, kPMColor_SkColorType);
             SkImageEncoder::EncodeFile(newRecord->fDifferencePath.c_str(), copy,
                                        SkImageEncoder::kPNG_Type, 100);