DM: don't crash on Mac.

BUG=skia:
R=reed@google.com, mtklein@google.com

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/177053005

git-svn-id: http://skia.googlecode.com/svn/trunk@13631 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/dm/DMReporter.cpp b/dm/DMReporter.cpp
index 1ff64c5..fb925ab 100644
--- a/dm/DMReporter.cpp
+++ b/dm/DMReporter.cpp
@@ -24,7 +24,7 @@
         status.appendf(", %d failed", failed);
     }
     status.appendf("\t[%s done]", name.c_str());
-    SkDebugf(status.c_str());
+    SkDebugf("%s", status.c_str());
 }
 
 int32_t Reporter::failed() const {