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

extensions/browser/file_reader.cc

Index: extensions/browser/file_reader.cc
diff --git a/extensions/browser/file_reader.cc b/extensions/browser/file_reader.cc
index c5deb9b646e071cc844cceb9ec57922b35afab31..9cb7939768787e2163a974415449763b920d6580 100644
--- a/extensions/browser/file_reader.cc
+++ b/extensions/browser/file_reader.cc
@@ -8,6 +8,8 @@
 #include "base/files/file_util.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "content/public/browser/browser_thread.h"
+#include "net/base/filename_util.h"
+#include "url/gurl.h"
 
 using content::BrowserThread;
 
@@ -28,6 +30,8 @@ FileReader::~FileReader() {}
 void FileReader::ReadFileOnBackgroundThread() {
   std::unique_ptr<std::string> data(new std::string());
   bool success = base::ReadFileToString(resource_.GetFilePath(), data.get());
+  GURL file_url = net::FilePathToFileURL(resource_.GetFilePath());
   origin_task_runner_->PostTask(
-      FROM_HERE, base::Bind(callback_, success, base::Passed(std::move(data))));
+      FROM_HERE,
+      base::Bind(callback_, success, file_url, base::Passed(std::move(data))));
 }