Fix and enable warning C4244 (Conversion from 'type1' to 'type2', possible loss of data)

Change-Id: Id0e06d7d6600344d858f00dabc219d79289bbc82
Reviewed-on: https://chromium-review.googlesource.com/265020
Tested-by: Minmin Gong <mgong@microsoft.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
diff --git a/util/shader_utils.cpp b/util/shader_utils.cpp
index 9bc41ae..4a71017 100644
--- a/util/shader_utils.cpp
+++ b/util/shader_utils.cpp
@@ -22,7 +22,7 @@
     std::string result;
 
     stream.seekg(0, std::ios::end);
-    result.reserve(stream.tellg());
+    result.reserve(static_cast<unsigned int>(stream.tellg()));
     stream.seekg(0, std::ios::beg);
 
     result.assign((std::istreambuf_iterator<char>(stream)), std::istreambuf_iterator<char>());