Fix double delete with invariant varyings.

The compiler would leave some TString variables lying around
after the pool gets released, leading to a potential crash.

BUG=angle:846

Change-Id: I484ed9b14bba9bf653f6ed4001ae79f87791b0dd
Reviewed-on: https://chromium-review.googlesource.com/232780
Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
diff --git a/src/compiler/translator/util.cpp b/src/compiler/translator/util.cpp
index 8cc06a6..42a995e 100644
--- a/src/compiler/translator/util.cpp
+++ b/src/compiler/translator/util.cpp
@@ -307,7 +307,7 @@
         break;
       case EvqVaryingIn:
       case EvqVaryingOut:
-        if (mSymbolTable.isVaryingInvariant(name))
+        if (mSymbolTable.isVaryingInvariant(std::string(name.c_str())))
         {
             variable->isInvariant = true;
         }