Fix a warning in PictureBenchmark.

Forgot to change from false to NULL. False does the right thing,
but gives a warning. Fix the warning.

Review URL: https://codereview.appspot.com/6570049

git-svn-id: http://skia.googlecode.com/svn/trunk@5666 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/tools/PictureBenchmark.cpp b/tools/PictureBenchmark.cpp
index 0b4f56e..fbf1585 100644
--- a/tools/PictureBenchmark.cpp
+++ b/tools/PictureBenchmark.cpp
@@ -85,7 +85,7 @@
         fRenderer->setup();
 
         timer->start();
-        fRenderer->render(false);
+        fRenderer->render(NULL);
         timer->truncatedEnd();
 
         // Finishes gl context