Remove canvas::NewRaster, and rename surface::NewRasterPMColor to N32Premul

patch from issue 781403002 at patchset 20001 (http://crrev.com/781403002#ps20001)

BUG=skia:
TBR=
re-landing after chrome fixes have landed

Review URL: https://codereview.chromium.org/784223007
diff --git a/gm/fatpathfill.cpp b/gm/fatpathfill.cpp
index ba6fffe..176c7bf 100644
--- a/gm/fatpathfill.cpp
+++ b/gm/fatpathfill.cpp
@@ -16,7 +16,7 @@
 #define REPEAT_LOOP 5
 
 static SkSurface* new_surface(int width, int height) {
-    return SkSurface::NewRasterPMColor(width, height);
+    return SkSurface::NewRasterN32Premul(width, height);
 }
 
 static void draw_pixel_centers(SkCanvas* canvas) {