Adds support for POST request with bodies on WKWebView.

ios/web/web_state/ui/crw_wk_script_message_router.mm

 // Copyright 2014 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/web/web_state/ui/crw_wk_script_message_router.h"
 
 #import "base/logging.h"
 #import "base/mac/scoped_nsobject.h"
 
 @interface CRWWKScriptMessageRouter ()<WKScriptMessageHandler>
@@ skipping 82 matching lines @@
     ((void (^)(WKScriptMessage*))handler)(message);
   }
 }
 
 #pragma mark -
 #pragma mark Implementation
 
 - (void)tryRemoveScriptMessageHandlerForName:(NSString*)messageName
                                      webView:(WKWebView*)webView {
   NSMapTable* webViewToHandlerMap = [_handlers objectForKey:messageName];
-  if (![webViewToHandlerMap objectForKey:webView])
+  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];
   } else {
     [webViewToHandlerMap removeObjectForKey:webView];
   }
 }
 
 @end