replace SkBitmap::Config with SkColorType in gms

add helper installMaskPixels() to SkBitmap

BUG=skia:
R=halcanary@google.com

Author: reed@google.com

Review URL: https://codereview.chromium.org/169913003

git-svn-id: http://skia.googlecode.com/svn/trunk@13482 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gm/shadertext2.cpp b/gm/shadertext2.cpp
index dcff3c6..1e6ae5c 100644
--- a/gm/shadertext2.cpp
+++ b/gm/shadertext2.cpp
@@ -11,8 +11,8 @@
 
 namespace skiagm {
 
-static void makebm(SkBitmap* bm, SkBitmap::Config config, int w, int h) {
-    bm->allocConfigPixels(config, w, h);
+static void makebm(SkBitmap* bm, int w, int h) {
+    bm->allocN32Pixels(w, h);
     bm->eraseColor(SK_ColorTRANSPARENT);
 
     SkCanvas    canvas(*bm);
@@ -92,7 +92,7 @@
 
         static SkBitmap bmp;
         if (bmp.isNull()) {
-            makebm(&bmp, SkBitmap::kARGB_8888_Config, kPointSize / 2, kPointSize / 2);
+            makebm(&bmp, kPointSize / 2, kPointSize / 2);
         }
 
         SkAutoTUnref<SkShader> shader(SkShader::CreateBitmapShader(bmp,