Add a helpful error in case web-inaccessible request.

chrome/renderer/extensions/extension_resource_request_policy.cc

 // Copyright (c) 2012 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/renderer/extensions/extension_resource_request_policy.h"
 
 #include "base/command_line.h"
 #include "base/logging.h"
+#include "base/stringprintf.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/url_constants.h"
 #include "chrome/common/extensions/extension.h"
 #include "chrome/common/extensions/extension_set.h"
 #include "googleurl/src/gurl.h"
+#include "third_party/WebKit/Source/WebKit/chromium/public/WebConsoleMessage.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebDocument.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebFrame.h"
+#include "third_party/WebKit/Source/WebKit/chromium/public/platform/WebString.h"
 
 // static
 bool ExtensionResourceRequestPolicy::CanRequestResource(
     const GURL& resource_url,
-    const WebKit::WebFrame* frame,
+    WebKit::WebFrame* frame,
     const ExtensionSet* loaded_extensions) {
   CHECK(resource_url.SchemeIs(chrome::kExtensionScheme));
 
   const Extension* extension =
       loaded_extensions->GetExtensionOrAppByURL(ExtensionURLInfo(resource_url));
   if (!extension) {
     // Allow the load in the case of a non-existent extension. We'll just get a
     // 404 from the browser process.
     return true;
   }
@@ skipping 21 matching lines @@
   // - chrome-extension:// (for legacy reasons -- some extensions interop)
   // - devtools (chrome-extension:// URLs are loaded into frames of devtools
   //     to support the devtools extension APIs)
   if (!CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kDisableExtensionsResourceWhitelist) &&
       !frame_url.is_empty() &&
       !frame_url.SchemeIs(chrome::kExtensionScheme) &&
       !(page_url.SchemeIs(chrome::kChromeDevToolsScheme) &&
           !extension->devtools_url().is_empty()) &&
       !extension->IsResourceWebAccessible(resource_url.path())) {
-    LOG(ERROR) << "Denying load of " << resource_url.spec() << " which "
-               << "is not a web accessible resource.";
+    std::string message = base::StringPrintf(
+        "Denying load of %s. Resources must be listed in the "
+        "web_accessible_resources manifest key in order to be loaded by web "
+        "pages.",
+        resource_url.spec().c_str());
+    frame->addMessageToConsole(
+        WebKit::WebConsoleMessage(WebKit::WebConsoleMessage::LevelError,
+                                  WebKit::WebString::fromUTF8(message)));
     return false;
   }
 
   return true;
 }
 
 ExtensionResourceRequestPolicy::ExtensionResourceRequestPolicy() {
 }