Make URLDataSource::GetSource() const.

chrome/browser/ui/webui/screenshot_source.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/browser/ui/webui/screenshot_source.h"
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/file_util.h"
 #include "base/files/file_path.h"
@@ skipping 121 matching lines @@
     if (!file_util::GetTempDir(directory)) {
       LOG(ERROR) << "Failed to find temporary directory.";
       return false;
     }
   }
   return true;
 }
 
 #endif
 
-std::string ScreenshotSource::GetSource() {
+std::string ScreenshotSource::GetSource() const {
   return chrome::kChromeUIScreenshotPath;
 }
 
 void ScreenshotSource::StartDataRequest(
   const std::string& path,
   bool is_incognito,
   const content::URLDataSource::GotDataCallback& callback) {
   SendScreenshot(path, callback);
 }
 
@@ skipping 110 matching lines @@
 void ScreenshotSource::CacheAndSendScreenshot(
     const std::string& screenshot_path,
     const content::URLDataSource::GotDataCallback& callback,
     ScreenshotDataPtr bytes) {
   // Strip the query from the screenshot path.
   std::string path = screenshot_path.substr(
       0, screenshot_path.find_first_of("?"));
   cached_screenshots_[path] = bytes;
   callback.Run(new base::RefCountedBytes(*bytes));
 }