[turbofan] Always check that we make progress in the Typer.

Turn the DCHECK in the Typer into a CHECK, and don't silently continue
in production. This way we know that we will always make progress
towards the fixpoint.

R=jarin@chromium.org, rossberg@chromium.org

Review URL: https://codereview.chromium.org/1422893003

Cr-Commit-Position: refs/heads/master@{#31568}

src/compiler/typer.cc

@@ -272,10 +272,10 @@ class Typer::Visitor : public Reducer {
         current = Weaken(node, current, previous);
       }
 
-      DCHECK(previous->Is(current));
+      CHECK(previous->Is(current));
 
       NodeProperties::SetType(node, current);
-      if (!(previous->Is(current) && current->Is(previous))) {
+      if (!current->Is(previous)) {
         // If something changed, revisit all uses.
         return Changed(node);
       }