Revert of Revert of Rename kPMColor_SkColorType to kN32_SkColorType.

tools/skpdiff/SkPMetric.cpp

Index: tools/skpdiff/SkPMetric.cpp
diff --git a/tools/skpdiff/SkPMetric.cpp b/tools/skpdiff/SkPMetric.cpp
index ed807636b63da0694164c6d1e82e9bff93e9842f..beba4974b770aefaeba6b7a2280de01b7c665517 100644
--- a/tools/skpdiff/SkPMetric.cpp
+++ b/tools/skpdiff/SkPMetric.cpp
@@ -125,8 +125,8 @@
 /// Converts a 8888 bitmap to LAB color space and puts it into the output
 static bool bitmap_to_cielab(const SkBitmap* bitmap, ImageLAB* outImageLAB) {
     SkBitmap bm8888;
-    if (bitmap->colorType() != kPMColor_SkColorType) {
-        if (!bitmap->copyTo(&bm8888, kPMColor_SkColorType)) {
+    if (bitmap->colorType() != kN32_SkColorType) {
+        if (!bitmap->copyTo(&bm8888, kN32_SkColorType)) {
             return false;
         }
         bitmap = &bm8888;