Fix linkage.html failures on Mac.

The failure is due to when we initialize variables to 0, we re-create
the struct TType, and it contains a different unique id from the
original struct TType, thus leading to a different hashed name.

BUG=chromium:641129
TEST=webgl_conformance,webgl2_conformance

Change-Id: I267b97fa496f55ea59dacee93af8f6a90f3e66cb
Reviewed-on: https://chromium-review.googlesource.com/409602
Commit-Queue: Zhenyao Mo <zmo@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
diff --git a/src/compiler/translator/InitializeVariables.h b/src/compiler/translator/InitializeVariables.h
index 8083577..9a34245 100644
--- a/src/compiler/translator/InitializeVariables.h
+++ b/src/compiler/translator/InitializeVariables.h
@@ -12,11 +12,20 @@
 namespace sh
 {
 class TIntermNode;
+class TSymbolTable;
 
 typedef std::vector<sh::ShaderVariable> InitVariableList;
 
-// This function cannot currently initialize structures containing arrays for an ESSL 1.00 backend.
-void InitializeVariables(TIntermNode *root, const InitVariableList &vars);
+// Currently this function is only capable of initializing variables of basic types,
+// array of basic types, or struct of basic types.
+// For now it is used for the following two scenarios:
+//   1. initializing gl_Position;
+//   2. initializing ESSL 3.00 shaders' output variables (which might be structs).
+// Specifically, it's not feasible to make it work for local variables because if their
+// types are structs, we can't look into TSymbolTable to find the TType data.
+void InitializeVariables(TIntermNode *root,
+                         const InitVariableList &vars,
+                         const TSymbolTable &symbolTable);
 }  // namespace sh
 
 #endif  // COMPILER_TRANSLATOR_INITIALIZEVARIABLES_H_