Fix crash when querying a runtime config that is defined in environment

Fix crash when querying a runtime config in case when there's no
skia.conf file and the config variable is still defined in the
environment.

Runs the added SkRTConf::UnitTest test as part of new "UnitTest" test.

Previous version of the patch failed Windows build due to setenv usage.
On Windows, use _putenv_s instead.

BUG=skia:1494
R=bsalomon@google.com, humper@google.com

Author: kkinnunen@nvidia.com

Review URL: https://chromiumcodereview.appspot.com/23174002

git-svn-id: http://skia.googlecode.com/svn/trunk/include@10715 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/utils/SkRTConf.h b/utils/SkRTConf.h
index ea6e99e..dc1f461 100644
--- a/utils/SkRTConf.h
+++ b/utils/SkRTConf.h
@@ -73,6 +73,9 @@
     void possiblyDumpFile() const;
     void validate() const;
     template <typename T> void set(const char *confname, T value);
+#ifdef SK_SUPPORT_UNITTEST
+    static void UnitTest();
+#endif
 private:
     template<typename T> friend class SkRTConf;
 
@@ -82,6 +85,9 @@
     SkTDArray<SkString *> fConfigFileKeys, fConfigFileValues;
     typedef SkTDict< SkTDArray<SkRTConfBase *> * > ConfMap;
     ConfMap fConfs;
+#ifdef SK_SUPPORT_UNITTEST
+    SkRTConfRegistry(bool);
+#endif
 };
 
 // our singleton registry