Adds MailtoURLRewriterObserver to MailtoURLRewriter

ios/chrome/browser/web/mailto_url_rewriter.mm

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ios/chrome/browser/web/mailto_url_rewriter.h"
 
 #import "base/logging.h"
 #import "ios/chrome/browser/web/mailto_handler.h"
 #import "ios/chrome/browser/web/mailto_handler_gmail.h"
 #import "ios/chrome/browser/web/mailto_handler_system_mail.h"
@@ skipping 34 matching lines @@
 - (void)migrateLegacyOptions;
 
 // For users who have not made an explicit choice (kMailtoDefaultHandlerKey
 // not set), if Gmail is detected, make an explicit choice for the user to
 // use Gmail app as the default mailto: handler.
 - (void)autoDefaultToGmailIfInstalled;
 
 @end
 
 @implementation MailtoURLRewriter
+@synthesize observer = _observer;
 @synthesize handlers = _handlers;
 
 + (NSString*)systemMailApp {
   // This is the App Store ID for Apple Mail app.
   // See https://itunes.apple.com/us/app/mail/id1108187098?mt=8
   return @"1108187098";
 }
 
 - (instancetype)init {
   self = [super init];
@@ skipping 18 matching lines @@
 }
 
 - (NSString*)defaultHandlerID {
   NSString* value = [[NSUserDefaults standardUserDefaults]
       stringForKey:kMailtoDefaultHandlerKey];
   return value ? value : [[self class] systemMailApp];
 }
 
 - (void)setDefaultHandlerID:(NSString*)appStoreID {
   DCHECK([appStoreID length]);
-  [[NSUserDefaults standardUserDefaults] setObject:appStoreID
-                                            forKey:kMailtoDefaultHandlerKey];
+  NSUserDefaults* defaults = [NSUserDefaults standardUserDefaults];
+  if ([appStoreID
+          isEqualToString:[defaults objectForKey:kMailtoDefaultHandlerKey]])
+    return;
+  [defaults setObject:appStoreID forKey:kMailtoDefaultHandlerKey];
+  [_observer rewriterDidChange:self];
+}
+
+- (NSString*)defaultHandlerName {
+  NSString* handlerID = [self defaultHandlerID];
+  MailtoHandler* handler = _handlers[handlerID];
+  return [handler appName];
 }
 
 - (NSString*)rewriteMailtoURL:(const GURL&)gURL {
   NSString* value = [self defaultHandlerID];
   if ([value length]) {
     MailtoHandler* handler = _handlers[value];
     if (handler) {
       return [handler rewriteMailtoURL:gURL];
     }
   }
@@ skipping 92 matching lines @@
   if ([defaults objectForKey:kMailtoDefaultHandlerKey])
     return;
 
   NSString* const kGmailAppStoreID = @"422689480";
   MailtoHandler* gmailHandler = _handlers[kGmailAppStoreID];
   if ([gmailHandler isAvailable])
     [defaults setObject:kGmailAppStoreID forKey:kMailtoDefaultHandlerKey];
 }
 
 @end