Split TIntermInvariantDeclaration from TIntermAggregate

This change is pure refactoring and doesn't fix bugs related to
invariant declarations. Invariant declarations are supposed to accept
a list of identifiers, but this refactoring keeps the current behavior
of only accepting a single identifier in an invariant declaration.
When the bug will be fixed, the new TIntermInvariantDeclaration class
that now has only a single child node can be changed so that it may
have multiple children.

TIntermAggregate is still used for function calls, function
prototypes and function parameter lists.

BUG=angleproject:1490
TEST=angle_unittests

Change-Id: I3e22092c87e1c06445fd7e123d9922c2fcb59428
Reviewed-on: https://chromium-review.googlesource.com/419415
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/IntermTraverse.cpp b/src/compiler/translator/IntermTraverse.cpp
index e6be777..ab3ad15 100644
--- a/src/compiler/translator/IntermTraverse.cpp
+++ b/src/compiler/translator/IntermTraverse.cpp
@@ -71,6 +71,11 @@
     it->traverseBlock(this);
 }
 
+void TIntermInvariantDeclaration::traverse(TIntermTraverser *it)
+{
+    it->traverseInvariantDeclaration(this);
+}
+
 void TIntermDeclaration::traverse(TIntermTraverser *it)
 {
     it->traverseDeclaration(this);
@@ -504,6 +509,25 @@
         visitBlock(PostVisit, node);
 }
 
+void TIntermTraverser::traverseInvariantDeclaration(TIntermInvariantDeclaration *node)
+{
+    bool visit = true;
+
+    if (preVisit)
+    {
+        visit = visitInvariantDeclaration(PreVisit, node);
+    }
+
+    if (visit)
+    {
+        node->getSymbol()->traverse(this);
+        if (postVisit)
+        {
+            visitInvariantDeclaration(PostVisit, node);
+        }
+    }
+}
+
 // Traverse a declaration node.
 void TIntermTraverser::traverseDeclaration(TIntermDeclaration *node)
 {