Fix slow gm debug builds that are doing large path validation runs.

Add a new compile flag to allow path validation to be selectively
enabled instead of being always on.

Review URL: https://codereview.appspot.com/6734059

git-svn-id: http://skia.googlecode.com/svn/trunk@6036 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/include/config/SkUserConfig.h b/include/config/SkUserConfig.h
index 93dda70..79fdc7a 100644
--- a/include/config/SkUserConfig.h
+++ b/include/config/SkUserConfig.h
@@ -65,6 +65,14 @@
 //#define SK_DEBUG
 //#define SK_RELEASE
 
+/*  Skia has certain debug-only code that is extremely intensive even for debug
+    builds.  This code is useful for diagnosing specific issues, but is not
+    generally applicable, therefore it must be explicitly enabled to avoid
+    the performance impact. By default these flags are undefined, but can be
+    enabled by uncommenting them below.
+ */
+//#define SK_DEBUG_PATH
+
 /*  To assist debugging, Skia provides an instance counting utility in
     include/core/SkInstCount.h. This flag turns on and off that utility to
     allow instance count tracking in either debug or release builds. By