[turbofan] Test has been outsmarted by optimization.

The fast-prototype test has been outsmarted by constructor inlining
because the instantiation is been correctly optimized away. Internal
state introspection about prototype turning fast was upset by that.

R=bmeurer@chromium.org
BUG=v8:4544
LOG=n

Review URL: https://codereview.chromium.org/1474763007

Cr-Commit-Position: refs/heads/master@{#32338}

test/mjsunit/fast-prototype.js

@@ -50,8 +50,9 @@ function DoProtoMagic(proto, set__proto__) {
     (new Sub()).__proto__ = proto;
   } else {
     Sub.prototype = proto;
-    // Need to instantiate Sub to mark .prototype as prototype.
-    new Sub();
+    // Need to instantiate Sub to mark .prototype as prototype. Make sure the
+    // instantiated object is used so that the allocation is not optimized away.
+    %DebugPrint(new Sub());
   }
 }
 

test/mjsunit/mjsunit.status

@@ -161,9 +161,6 @@
   # Issue 4055: Scope chain length observed by debugger is off.
   'es6/generators-debug-scopes': [PASS, NO_VARIANTS],
 
-  # TODO(4544): Investigate why assumptions about fast properties break.
-  'fast-prototype': [PASS, NO_VARIANTS],
-
   # TODO(titzer): --always-opt incorrectly disables CrankShaft soft deopt points
   'result-table-min': [PASS, NO_VARIANTS],
   'result-table-max': [PASS, NO_VARIANTS],