[MR UI] Set dialog width in MediaRouterDialogDelegate::GetDialogSize() if not set

chrome/browser/ui/webui/media_router/media_router_dialog_controller_impl.cc

 // Copyright 2015 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.
 
 #include "chrome/browser/ui/webui/media_router/media_router_dialog_controller_impl.h"
 
 #include <memory>
 #include <string>
 #include <utility>
 #include <vector>
@@ skipping 61 matching lines @@
     return GURL(chrome::kChromeUIMediaRouterURL);
   }
 
   void GetWebUIMessageHandlers(
       std::vector<WebUIMessageHandler*>* handlers) const override {
     // MediaRouterUI adds its own message handlers.
   }
 
   void GetDialogSize(gfx::Size* size) const override {
     DCHECK(size);
+    // We set the dialog width if it's not set, so that the dialog is
+    // center-aligned horizontally when it appears.
+    if (size->width() != kWidth)
+      size->set_width(kWidth);
     // GetDialogSize() is called when the browser window resizes. We may want to
     // update the maximum height of the dialog and scale the WebUI to the new
     // height. |size| is not set because the dialog is auto-resizeable.
     controller_->UpdateMaxDialogSize();
   }
 
   std::string GetDialogArgs() const override {
     return std::string();
   }
 
@@ skipping 221 matching lines @@
       PresentationServiceDelegateImpl::FromWebContents(initiator());
   if (!create_connection_request.get()) {
     media_router_ui->InitWithDefaultMediaSource(initiator(), delegate);
   } else {
     media_router_ui->InitWithPresentationSessionRequest(
         initiator(), delegate, std::move(create_connection_request));
   }
 }
 
 }  // namespace media_router