Change old PRG to be SkLCGRandom; change new one to SkRandom

The goal here is to get people to start using the new random number
generator, while leaving the old one in place so we don't have to 
rebaseline GMs.

R=reed@google.com, bsalomon@google.com

Author: jvanverth@google.com

Review URL: https://chromiumcodereview.appspot.com/23576015

git-svn-id: http://skia.googlecode.com/svn/trunk@11169 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/bench/ShaderMaskBench.cpp b/bench/ShaderMaskBench.cpp
index d2f4e26..0e8e4bb 100644
--- a/bench/ShaderMaskBench.cpp
+++ b/bench/ShaderMaskBench.cpp
@@ -59,7 +59,7 @@
 
     virtual void onDraw(SkCanvas* canvas) {
         const SkIPoint dim = this->getSize();
-        SkMWCRandom rand;
+        SkRandom rand;
 
         SkPaint paint(fPaint);
         this->setupPaint(&paint);