remove (dumb) canvas::NewRaster, and rename surface::NewRasterPMColor to N32Premul

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

BUG=skia:

Review URL: https://codereview.chromium.org/790733003
diff --git a/tests/RecordDrawTest.cpp b/tests/RecordDrawTest.cpp
index 30be24c..2d9e90d 100644
--- a/tests/RecordDrawTest.cpp
+++ b/tests/RecordDrawTest.cpp
@@ -286,7 +286,7 @@
         bool fDrawImageRectCalled;
     };
 
-    SkAutoTUnref<SkSurface> surface(SkSurface::NewRasterPMColor(10, 10));
+    SkAutoTUnref<SkSurface> surface(SkSurface::NewRasterN32Premul(10, 10));
     surface->getCanvas()->clear(SK_ColorGREEN);
     SkAutoTUnref<SkImage> image(surface->newImageSnapshot());