[turbofan] Don't try to inline our builtins.

R=mstarzinger@chromium.org
BUG=v8:4493
LOG=n

Review URL: https://codereview.chromium.org/1432223002

Cr-Commit-Position: refs/heads/master@{#31944}

src/compiler/js-inlining-heuristic.cc

@@ -48,6 +48,9 @@ Reduction JSInliningHeuristic::Reduce(Node* node) {
   // Built-in functions are handled by the JSBuiltinReducer.
   if (function->shared()->HasBuiltinFunctionId()) return NoChange();
 
+  // Don't inline builtins.
+  if (function->shared()->IsBuiltin()) return NoChange();
+
   // Quick check on source code length to avoid parsing large candidate.
   if (function->shared()->SourceSize() > FLAG_max_inlined_source_size) {
     return NoChange();