[ObjC ARC] Converts ios/web:web to ARC.

ios/web/web_state/ui/crw_wk_script_message_router.mm

Index: ios/web/web_state/ui/crw_wk_script_message_router.mm
diff --git a/ios/web/web_state/ui/crw_wk_script_message_router.mm b/ios/web/web_state/ui/crw_wk_script_message_router.mm
index ed13ddb0b878def502fbd03555fc35f32ee2a154..295ab0bd891506a364eb49a2f71d2c97311648d7 100644
--- a/ios/web/web_state/ui/crw_wk_script_message_router.mm
+++ b/ios/web/web_state/ui/crw_wk_script_message_router.mm
@@ -5,7 +5,10 @@
 #import "ios/web/web_state/ui/crw_wk_script_message_router.h"
 
 #include "base/logging.h"
-#import "base/mac/scoped_nsobject.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
 
 @interface CRWWKScriptMessageRouter ()<WKScriptMessageHandler>
 
@@ -13,23 +16,23 @@
 - (void)tryRemoveScriptMessageHandlerForName:(NSString*)messageName
                                      webView:(WKWebView*)webView;
 
+@property(nonatomic, weak, readwrite)
+    WKUserContentController* userContentController;
+
 @end
 
 @implementation CRWWKScriptMessageRouter {
   // Two level map of registed message handlers. Keys are message names and
   // values are more maps (where keys are web views and values are handlers).
-  base::scoped_nsobject<NSMutableDictionary> _handlers;
-  // Wrapped WKUserContentController.
-  base::scoped_nsobject<WKUserContentController> _userContentController;
+  NSMutableDictionary* _handlers;
 }
 
+// Wrapped WKUserContentController.
+@synthesize userContentController = _userContentController;
+
 #pragma mark -
 #pragma mark Interface
 
-- (WKUserContentController*)userContentController {
-  return _userContentController.get();
-}
-
 - (instancetype)init {
   NOTREACHED();
   return nil;
@@ -39,8 +42,8 @@
     (WKUserContentController*)userContentController {
   DCHECK(userContentController);
   if ((self = [super init])) {
-    _handlers.reset([[NSMutableDictionary alloc] init]);
-    _userContentController.reset([userContentController retain]);
+    _handlers = [[NSMutableDictionary alloc] init];
+    _userContentController = userContentController;
   }
   return self;
 }
@@ -100,12 +103,11 @@
 - (void)tryRemoveScriptMessageHandlerForName:(NSString*)messageName
                                      webView:(WKWebView*)webView {
   NSMapTable* webViewToHandlerMap = [_handlers objectForKey:messageName];
-  id handler = [webViewToHandlerMap objectForKey:webView];
+  NS_VALID_UNTIL_END_OF_SCOPE id handler =
+      [webViewToHandlerMap objectForKey:webView];
   if (!handler)
     return;
-  // Extend the lifetime of |handler| so removeScriptMessageHandlerForName: can
-  // be called from inside of |handler|.
-  [[handler retain] autorelease];
+
   if (webViewToHandlerMap.count == 1) {
     [_handlers removeObjectForKey:messageName];
     [_userContentController removeScriptMessageHandlerForName:messageName];