Add enable*Features functions in preparation for using them in content.

Source/WebKit/chromium/public/WebRuntimeFeatures.h

Index: Source/WebKit/chromium/public/WebRuntimeFeatures.h
diff --git a/Source/WebKit/chromium/public/WebRuntimeFeatures.h b/Source/WebKit/chromium/public/WebRuntimeFeatures.h
index 633b08d8432156f2133a7803669e44f6ed66cd30..e5c5232935e3d70ce2ad2b1d4a31c24ba6552ae4 100644
--- a/Source/WebKit/chromium/public/WebRuntimeFeatures.h
+++ b/Source/WebKit/chromium/public/WebRuntimeFeatures.h
@@ -41,6 +41,10 @@ namespace WebKit {
 // certain level of maturity.
 class WebRuntimeFeatures {
 public:
+    WEBKIT_EXPORT static void enableStableFeatures(bool);
+    WEBKIT_EXPORT static void enableExperimentalFeatures(bool);
+    WEBKIT_EXPORT static void enableTestOnlyFeatures(bool);
+
     WEBKIT_EXPORT static void enableDatabase(bool);
     WEBKIT_EXPORT static bool isDatabaseEnabled();