Clean up unnecessary use of TString

TString was being used in some places where it was not really needed.
Clean these up.

BUG=angleproject:2267
TEST=angle_unittests

Change-Id: Ib7fd26f9c6b6b885433c840a9520393908f1f902
Reviewed-on: https://chromium-review.googlesource.com/887068
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>
diff --git a/src/compiler/translator/OutputGLSLBase.cpp b/src/compiler/translator/OutputGLSLBase.cpp
index f04127f..74b38d2 100644
--- a/src/compiler/translator/OutputGLSLBase.cpp
+++ b/src/compiler/translator/OutputGLSLBase.cpp
@@ -678,8 +678,8 @@
 
 bool TOutputGLSLBase::visitUnary(Visit visit, TIntermUnary *node)
 {
-    TString preString;
-    TString postString = ")";
+    const char *preString  = "";
+    const char *postString = ")";
 
     switch (node->getOp())
     {
@@ -780,7 +780,7 @@
             UNREACHABLE();
     }
 
-    writeTriplet(visit, preString.c_str(), nullptr, postString.c_str());
+    writeTriplet(visit, preString, nullptr, postString);
 
     return true;
 }