Add CWVUserContentController which enables injecting JavaScripts.

ios/web_view/public/cwv_web_view_configuration.h

Index: ios/web_view/public/cwv_web_view_configuration.h
diff --git a/ios/web_view/public/cwv_web_view_configuration.h b/ios/web_view/public/cwv_web_view_configuration.h
index a2a7489b3c4cfe52c9aecddae946bd731bdc8f4d..6be74da2d139f6fc2f7dc114faa2c42b72720cc2 100644
--- a/ios/web_view/public/cwv_web_view_configuration.h
+++ b/ios/web_view/public/cwv_web_view_configuration.h
@@ -7,6 +7,7 @@
 
 #import <Foundation/Foundation.h>
 
+@class CWVUserContentController;
 @class CWVWebsiteDataStore;
 
 // Configuration used for creation of a CWVWebView.
@@ -20,9 +21,13 @@
 
 - (instancetype)init NS_UNAVAILABLE;
 
+// The user content controller to associate with web views created using this
+// configuration.
+@property(nonatomic, readonly) CWVUserContentController* userContentController;
+
 // YES if it is a configuration with persistent data store which stores all data
 // on disk.
-@property(readonly, getter=isPersistent) BOOL persistent;
+@property(nonatomic, readonly, getter=isPersistent) BOOL persistent;
 
 @end