Make RendererD3D a bit smaller.

Move some D3D11-specific stuff into Renderer11, and remove a few
virtual methods that weren't needed to be virtual.

BUG=angleproject:1369

Change-Id: Id37e7271ffc28b089dbea123dca70f38c1a06ffb
Reviewed-on: https://chromium-review.googlesource.com/345913
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
diff --git a/src/common/string_utils.h b/src/common/string_utils.h
index 131b17e..99e7187 100644
--- a/src/common/string_utils.h
+++ b/src/common/string_utils.h
@@ -13,6 +13,8 @@
 #include <string>
 #include <vector>
 
+#include "common/Optional.h"
+
 namespace angle
 {
 
@@ -44,6 +46,7 @@
 
 bool ReadFileToString(const std::string &path, std::string *stringOut);
 
+Optional<std::vector<wchar_t>> WidenString(size_t length, const char *cString);
 }
 
 #endif // LIBANGLE_STRING_UTILS_H_