Remove some UI->FILE->UI thread hops in ExecuteCodeFunction

extensions/browser/file_reader.h

Index: extensions/browser/file_reader.h
diff --git a/extensions/browser/file_reader.h b/extensions/browser/file_reader.h
index 9b391f8635be496d1792bfa6d52f4307aec29bc3..e78773bf175bdc4f5db80fdad9a65159984d9676 100644
--- a/extensions/browser/file_reader.h
+++ b/extensions/browser/file_reader.h
@@ -12,6 +12,8 @@
 #include "base/single_thread_task_runner.h"
 #include "extensions/common/extension_resource.h"
 
+class GURL;
+
 // This file defines an interface for reading a file asynchronously on a
 // background thread.
 // Consider abstracting out a FilePathProvider (ExtensionResource) and moving
@@ -19,7 +21,9 @@
 class FileReader : public base::RefCountedThreadSafe<FileReader> {
  public:
   // Reports success or failure and the data of the file upon success.
-  typedef base::Callback<void(bool, std::unique_ptr<std::string>)> Callback;
+  typedef base::Callback<
+      void(bool, const GURL& file_url, std::unique_ptr<std::string>)>
+      Callback;
 
   FileReader(const extensions::ExtensionResource& resource,
              const Callback& callback);