[DevTools] Shows Manifest file in Sources tab

content/renderer/manifest/manifest_manager.cc

 // 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.
 
 #include "content/renderer/manifest/manifest_manager.h"
 
 #include "base/bind.h"
 #include "base/strings/nullable_string16.h"
 #include "content/common/manifest_manager_messages.h"
 #include "content/public/renderer/render_frame.h"
@@ skipping 142 matching lines @@
     return;
   }
 
   ManifestUmaUtil::FetchSucceeded();
 
   ManifestParser parser(data, response.url(), document_url);
   parser.Parse();
 
   fetcher_.reset();
 
   for (const std::string& msg : parser.errors()) {

[pfeldman, 2016/01/08 01:54:06]

JSONReader actually has the error line and column, but they are not exposed.
It'd be great if we could plumb them all the way - should not be a big deal.

     blink::WebConsoleMessage message;
     message.level = blink::WebConsoleMessage::LevelError;
     message.text = blink::WebString::fromUTF8(msg);
+    message.url =
+        render_frame()->GetWebFrame()->document().manifestURL().string();
     render_frame()->GetWebFrame()->addMessageToConsole(message);
   }
 
   // Having errors while parsing the manifest doesn't mean the manifest parsing
   // failed. Some properties might have been ignored but some others kept.
   if (parser.failed()) {
     ResolveCallbacks(ResolveStateFailure);
     return;
   }
 
@@ skipping 12 matching lines @@
 
   pending_callbacks_.clear();
 
   for (std::list<GetManifestCallback>::const_iterator it = callbacks.begin();
        it != callbacks.end(); ++it) {
     it->Run(manifest);
   }
 }
 
 } // namespace content