Rename ConstantUnion to TConstantUnion.

This clarified that we're using the Pool allocator/deallocator for
this type.

BUG=angleproject:993

Change-Id: If8c95f6054d07291e7014be0d4e35766ba2e943b
Reviewed-on: https://chromium-review.googlesource.com/269131
Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
diff --git a/src/compiler/translator/OutputGLSLBase.cpp b/src/compiler/translator/OutputGLSLBase.cpp
index 13c6579..5bf6bb2 100644
--- a/src/compiler/translator/OutputGLSLBase.cpp
+++ b/src/compiler/translator/OutputGLSLBase.cpp
@@ -168,8 +168,8 @@
     }
 }
 
-const ConstantUnion *TOutputGLSLBase::writeConstantUnion(
-    const TType &type, const ConstantUnion *pConstUnion)
+const TConstantUnion *TOutputGLSLBase::writeConstantUnion(
+    const TType &type, const TConstantUnion *pConstUnion)
 {
     TInfoSinkBase &out = objSink();
 
@@ -386,7 +386,7 @@
                 TIntermConstantUnion *element = (*sit)->getAsConstantUnion();
                 ASSERT(element->getBasicType() == EbtInt);
                 ASSERT(element->getNominalSize() == 1);
-                const ConstantUnion& data = element->getUnionArrayPointer()[0];
+                const TConstantUnion& data = element->getUnionArrayPointer()[0];
                 ASSERT(data.getType() == EbtInt);
                 switch (data.getIConst())
                 {