Remove the usage of some c++11 library features

That were causing compilation error in Chromium Mac builds

BUG=angleproject:891

Change-Id: I45777451b300928e8c8d232a5b7ecffa7f1c3cbe
Reviewed-on: https://chromium-review.googlesource.com/299721
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tryjob-Request: Corentin Wallez <cwallez@chromium.org>
Tested-by: Corentin Wallez <cwallez@chromium.org>
diff --git a/util/shader_utils.cpp b/util/shader_utils.cpp
index 3d79a43..33f8bc6 100644
--- a/util/shader_utils.cpp
+++ b/util/shader_utils.cpp
@@ -12,7 +12,7 @@
 
 static std::string ReadFileToString(const std::string &source)
 {
-    std::ifstream stream(source);
+    std::ifstream stream(source.c_str());
     if (!stream)
     {
         std::cerr << "Failed to load shader file: " << source;