Remove vestigial legacy const handling from parser

src/parsing/parser.cc

Index: src/parsing/parser.cc
diff --git a/src/parsing/parser.cc b/src/parsing/parser.cc
index e3063d8b1fc251ddc5b493391e5fbb858ad097ad..daa0a2df6dcc3f944493a0fc7dd4632cf260a1db 100644
--- a/src/parsing/parser.cc
+++ b/src/parsing/parser.cc
@@ -1982,14 +1982,6 @@ Variable* Parser::Declare(Declaration* declaration,
   // RuntimeHidden_DeclareLookupSlot calls.
   declaration_scope->AddDeclaration(declaration);
 
-  if (mode == CONST_LEGACY && declaration_scope->is_script_scope()) {
-    // For global const variables we bind the proxy to a variable.
-    DCHECK(resolve);  // should be set by all callers
-    Variable::Kind kind = Variable::NORMAL;
-    var = new (zone()) Variable(declaration_scope, name, mode, kind,
-                                kNeedsInitialization, kNotAssigned);
-  }
-
   // If requested and we have a local variable, bind the proxy to the variable
   // at parse-time. This is used for functions (and consts) declared inside
   // statements: the corresponding function (or const) variable must be in the
@@ -2366,9 +2358,8 @@ Block* Parser::ParseVariableDeclarations(
           return nullptr;
         }
 
-        // 'let x' and (legacy) 'const x' initialize 'x' to undefined.
-        if (parsing_result->descriptor.mode == LET ||
-            parsing_result->descriptor.mode == CONST_LEGACY) {
+        // 'let x' initializes 'x' to undefined.
+        if (parsing_result->descriptor.mode == LET) {

[caitp (gmail), 2016/04/14 00:17:30]

This is not really the job of this CL, but this looks wrong, there shouldn't be
an implicit initializer for a let variable. Maybe a TODO() is in order?

[caitp (gmail), 2016/04/14 00:25:16]

eh, other vendors seem to behave the same, did the spec change? I thought these
were hole-y until assigned

[adamk, 2016/04/14 00:37:24]

Nope, nothing recent here. Let variables are hole-initialized when we enter the
scope (to throw TDZ errors as appropriate), and then undefined-initialized then
we reach the declaration. I would believe this changed during the genesis of
ES6, but this is definitely what the spec says now :)

           value = GetLiteralUndefined(position());
         }
       }