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/intermOut.cpp b/src/compiler/translator/intermOut.cpp
index 07c50f0..3833f5a 100644
--- a/src/compiler/translator/intermOut.cpp
+++ b/src/compiler/translator/intermOut.cpp
@@ -265,7 +265,7 @@
         OutputTreeText(out, intermConstantUnion, mDepth + 1);
 
         // The following code finds the field name from the constant union
-        const ConstantUnion *constantUnion = intermConstantUnion->getUnionArrayPointer();
+        const TConstantUnion *constantUnion = intermConstantUnion->getUnionArrayPointer();
         const TStructure *structure = node->getLeft()->getType().getStruct();
         const TInterfaceBlock *interfaceBlock = node->getLeft()->getType().getInterfaceBlock();
         ASSERT(structure || interfaceBlock);