Move ReadFileToString to the base namespace.

chrome_frame/test/navigation_test.cc

Index: chrome_frame/test/navigation_test.cc
diff --git a/chrome_frame/test/navigation_test.cc b/chrome_frame/test/navigation_test.cc
index 2f5ab339c5694eac34bfad52558ee789bca60d44..fca132c17afb68458be4ee585ca418783d619162 100644
--- a/chrome_frame/test/navigation_test.cc
+++ b/chrome_frame/test/navigation_test.cc
@@ -871,7 +871,7 @@ TEST_F(FullTabDownloadTest, CF_DownloadFileFromPost) {
   LaunchIENavigateAndLoop(src_url, kChromeFrameVeryLongNavigationTimeout);
 
   std::string data;
-  EXPECT_TRUE(file_util::ReadFileToString(temp_file_path, &data));
+  EXPECT_TRUE(base::ReadFileToString(temp_file_path, &data));
   EXPECT_EQ("hello", data);
   file_util::DieFileDie(temp_file_path, false);
 }