Split TIntermBlock from TIntermAggregate

The new TIntermBlock node class replaces TIntermAggregate nodes with
the EOpSequence op. It represents the root node of the tree which is
a list of declarations and function definitions, and any code blocks
that can be denoted by curly braces. These include function and loop
bodies, and if-else branches.

This change enables a bunch of more compile-time type checking, and
makes the AST code easier to understand and less error-prone.

The PostProcess step that used to be done to ensure that the root node
is TIntermAggregate is removed in favor of making sure that the root
node is a TIntermBlock in the glslang.y parsing code.

Intermediate output formatting is improved to print the EOpNull error
in a clearer way.

After this patch, TIntermAggregate is still used for function
definitions, function prototypes, function parameter lists, function
calls, variable and invariant declarations and the comma (sequence)
operator.

BUG=angleproject:1490
TEST=angle_unittests, angle_end2end_tests

Change-Id: I04044affff979a11577bc1fe75d747e538b799c8
Reviewed-on: https://chromium-review.googlesource.com/393726
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
diff --git a/src/compiler/translator/InitializeVariables.cpp b/src/compiler/translator/InitializeVariables.cpp
index 235f498..d44f2fa 100644
--- a/src/compiler/translator/InitializeVariables.cpp
+++ b/src/compiler/translator/InitializeVariables.cpp
@@ -45,8 +45,6 @@
     bool visitChildren = !mCodeInserted;
     switch (node->getOp())
     {
-      case EOpSequence:
-        break;
       case EOpFunction:
       {
         // Function definition.
@@ -55,7 +53,7 @@
         {
             TIntermSequence *sequence = node->getSequence();
             ASSERT(sequence->size() == 2);
-            TIntermAggregate *body = (*sequence)[1]->getAsAggregate();
+            TIntermBlock *body = (*sequence)[1]->getAsBlock();
             ASSERT(body);
             insertInitCode(body->getSequence());
             mCodeInserted = true;