Add a policy to re-enable deprecated web platform features.

webkit/common/webpreferences.h

Index: webkit/common/webpreferences.h
diff --git a/webkit/common/webpreferences.h b/webkit/common/webpreferences.h
index f5dc458d5cc053aeca0535f56b12d3e7a0dbff70..3e85faf081315237072804c51c8b0dbe98e3d391 100644
--- a/webkit/common/webpreferences.h
+++ b/webkit/common/webpreferences.h
@@ -42,6 +42,12 @@ enum EditingBehavior {
   EDITING_BEHAVIOR_LAST = EDITING_BEHAVIOR_ANDROID
 };
 
+// Enum of features that can be re-enabled via WebPreferences.
+enum DeprecatedFeature {
+  DEPRECATED_FEATURE_SHOW_MODAL_DIALOG,
+  DEPRECATED_FEATURE_COUNT,
+};
+
 
 // The ISO 15924 script code for undetermined script aka Common. It's the
 // default used on WebKit's side to get/set a font setting when no script is
@@ -161,6 +167,10 @@ struct WEBKIT_COMMON_EXPORT WebPreferences {
   // pepper plugins. Defaults to false.
   bool pepper_accelerated_video_decode_enabled;
 
+  // A bitset indicating which deprecated features to enable in the renderer.
+  // See enum DeprecatedFeature for valid values.
+  std::vector<bool> deprecated_features_to_enable;
+
 #if defined(OS_ANDROID)
   bool text_autosizing_enabled;
   float font_scale_factor;