Add a public API to enable/disable blink runtime features by name

public/web/WebRuntimeFeatures.h

Index: public/web/WebRuntimeFeatures.h
diff --git a/public/web/WebRuntimeFeatures.h b/public/web/WebRuntimeFeatures.h
index c46aeb124a8e5e0f4238925868a1a91afd6890c0..d413d31fe31273f945c8769a88cdac4b99bee122 100644
--- a/public/web/WebRuntimeFeatures.h
+++ b/public/web/WebRuntimeFeatures.h
@@ -35,6 +35,8 @@
 
 namespace WebKit {
 
+class WebString;
+
 // This class is used to enable runtime features of Blink.
 // All features are disabled by default.
 // Most clients should call enableStableFeatures() to enable
@@ -44,6 +46,7 @@ public:
     WEBKIT_EXPORT static void enableStableFeatures(bool);
     WEBKIT_EXPORT static void enableExperimentalFeatures(bool);
     WEBKIT_EXPORT static void enableTestOnlyFeatures(bool);
+    WEBKIT_EXPORT static bool setFeatureEnabled(const WebString&, bool);
 
     // FIXME: Delete after removing all callers in Content.
     static void enableFullScreenAPI(bool enable) { enableFullscreen(enable); }