[parser] Minor Token::INIT cleanup.

Here the token cannot be Token::INIT since it's coming from the Scanner. Scanner
never returns Token::INIT, and Token::INIT is only used internally in the AST.

Bug: 
Change-Id: I185e6d3330651b7ee784b916908e7d8d803b63b9
Reviewed-on: https://chromium-review.googlesource.com/616282
Commit-Queue: Marja Hölttä <marja@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47390}

src/parsing/parser-base.h

@@ -2887,8 +2887,7 @@ ParserBase<Impl>::ParseAssignmentExpression(bool accept_IN, bool* ok) {
     // Check if the right hand side is a call to avoid inferring a
     // name if we're dealing with "a = function(){...}();"-like
     // expression.
-    if ((op == Token::INIT || op == Token::ASSIGN) &&
-        (!right->IsCall() && !right->IsCallNew())) {
+    if (op == Token::ASSIGN && !right->IsCall() && !right->IsCallNew()) {
       fni_->Infer();
     } else {
       fni_->RemoveLastFunction();
@@ -2904,6 +2903,7 @@ ParserBase<Impl>::ParseAssignmentExpression(bool accept_IN, bool* ok) {
     return impl()->RewriteAssignExponentiation(expression, right, pos);
   }
 
+  DCHECK_NE(op, Token::INIT);
   ExpressionT result = factory()->NewAssignment(op, expression, right, pos);
 
   if (is_destructuring_assignment) {