use some helper Make functions to initialize SkImageInfo

BUG=
R=halcanary@google.com, scroggo@google.com

Author: reed@google.com

Review URL: https://codereview.chromium.org/137993012

git-svn-id: http://skia.googlecode.com/svn/trunk@13081 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gm/srcmode.cpp b/gm/srcmode.cpp
index 666a36b..6aa236f 100644
--- a/gm/srcmode.cpp
+++ b/gm/srcmode.cpp
@@ -117,12 +117,7 @@
 
     static SkSurface* compat_surface(SkCanvas* canvas, const SkISize& size,
                                      bool skipGPU) {
-        SkImageInfo info = {
-            size.width(),
-            size.height(),
-            kPMColor_SkColorType,
-            kPremul_SkAlphaType
-        };
+        SkImageInfo info = SkImageInfo::MakeN32Premul(size);
 #if SK_SUPPORT_GPU
         SkBaseDevice* dev = canvas->getDevice();
         if (!skipGPU && dev->accessRenderTarget()) {