[parser] Harden DCHECK into CHECK in parser

A DCHECK is guarding something which has previously been a memory
integrity issue. It should be cheap to run. This patch makes it
into a CHECK.

BUG=chromium:658267

Review-Url: https://codereview.chromium.org/2584223002
Cr-Commit-Position: refs/heads/master@{#41825}

src/parsing/func-name-inferrer.cc

@@ -46,8 +46,8 @@ void FuncNameInferrer::PushVariableName(const AstRawString* name) {
 
 void FuncNameInferrer::RemoveAsyncKeywordFromEnd() {
   if (IsOpen()) {
-    DCHECK(names_stack_.length() > 0);
-    DCHECK(names_stack_.last().name->IsOneByteEqualTo("async"));
+    CHECK(names_stack_.length() > 0);
+    CHECK(names_stack_.last().name->IsOneByteEqualTo("async"));
     names_stack_.RemoveLast();
   }
 }