Check modulo values passed to GM.

R=reed@google.com
Review URL: https://codereview.appspot.com/6820073

git-svn-id: http://skia.googlecode.com/svn/trunk@6248 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gm/gmmain.cpp b/gm/gmmain.cpp
index a4c88b1..e9c265b 100644
--- a/gm/gmmain.cpp
+++ b/gm/gmmain.cpp
@@ -816,7 +816,7 @@
 #if SK_SUPPORT_GPU
 SkAutoTUnref<GrContext> gGrContext;
 /**
- * Sets the global GrContext, accessible by indivual GMs
+ * Sets the global GrContext, accessible by individual GMs
  */
 static void SetGr(GrContext* grContext) {
     SkSafeRef(grContext);
@@ -953,6 +953,10 @@
                 continue;
             }
             moduloDivisor = atoi(*argv);
+            if (moduloRemainder < 0 || moduloDivisor <= 0 || moduloRemainder >= moduloDivisor) {
+                SkDebugf("invalid modulo values.");
+                return -1;
+            }
         } else if (strcmp(*argv, "--nopdf") == 0) {
             doPDF = false;
         } else if (strcmp(*argv, "--nopipe") == 0) {