change gm option from -config to --config, to match the double-dash convention of
all of its other options.
Review URL: https://codereview.appspot.com/6337044

git-svn-id: http://skia.googlecode.com/svn/trunk@4307 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gm/gmmain.cpp b/gm/gmmain.cpp
index 877d0af..0c31975 100644
--- a/gm/gmmain.cpp
+++ b/gm/gmmain.cpp
@@ -717,7 +717,7 @@
 static void usage(const char * argv0) {
     SkDebugf("%s\n", argv0);
     SkDebugf("    [-w writePath] [-r readPath] [-d diffPath] [-i resourcePath]\n");
-    SkDebugf("    [-config ");
+    SkDebugf("    [--config ");
     for (size_t i = 0; i < SK_ARRAY_COUNT(gRec); ++i) {
         if (i > 0) {
             SkDebugf("|");
@@ -890,7 +890,7 @@
             }
         } else if (strcmp(*argv, "--notexturecache") == 0) {
             disableTextureCache = true;
-        } else if (strcmp(*argv, "-config") == 0) {
+        } else if (strcmp(*argv, "--config") == 0) {
             argv++;
             if (argv < stop) {
                 int index = findConfig(*argv);
@@ -905,7 +905,7 @@
                     return -1;
                 }
             } else {
-                SkDebugf("missing arg for -config\n");
+                SkDebugf("missing arg for --config\n");
                 usage(commandName);
                 return -1;
             }