Add sendWebKitMessage JavaScript function to common.js

This function will be reused by features in order to communicate back to
the native application from any arbitrary frame.

Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I729c1c1b5faba803b7b334ae73674e5b017ef587
Reviewed-on: https://chromium-review.googlesource.com/896615
Commit-Queue: Mike Dougherty <michaeldo@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#533904}

ios/web/web_state/js/resources/common.js

@@ -703,4 +703,20 @@ __gCrWeb['common'] = __gCrWeb.common;
     return new URL(url_one).origin == new URL(url_two).origin;
   }
 
+  /**
+   * Posts |message| to the webkit message handler specified by |handlerName|.
+   *
+   * @param {string} handlerName The name of the webkit message handler.
+   * @param {Object} message The message to post to the handler.
+   */
+  __gCrWeb.common.sendWebKitMessage = function(handlerName, message) {
+    // A web page can override |window.webkit| with any value. Deleting the
+    // object ensures that original and working implementation of
+    // window.webkit is restored.
+    var oldWebkit = window.webkit;
+    delete window['webkit'];
+    window.webkit.messageHandlers[handlerName].postMessage(message);
+    window.webkit = oldWebkit;
+ }
+
 }());  // End of anonymous object

ios/web/web_state/js/resources/message.js

@@ -77,16 +77,10 @@ __gCrWeb['message'] = __gCrWeb.message;
       delete Object.prototype.toJSON;
 
     queueObject.queue.forEach(function(command) {
-        // A web page can override |window.webkit| with any value. Deleting the
-        // object ensures that original and working implementation of
-        // window.webkit is restored.
-        var oldWebkit = window.webkit;
-        delete window['webkit'];
-        window.webkit.messageHandlers[queueObject.scheme].postMessage({
-            "crwCommand": command,
-            "crwWindowId": window.top.__gCrWeb['windowId']
-        });
-        window.webkit = oldWebkit;
+      __gCrWeb.common.sendWebKitMessage(queueObject.scheme, {
+        "crwCommand": command,
+        "crwWindowId": window.top.__gCrWeb['windowId']
+      });
     });
     queueObject.reset();