Revert of [ic] Experiment: disable map-specific handler cache. (patchset #1...

Revert of [ic] Experiment: disable map-specific handler cache. (patchset #1 id:1 of https://codereview.chromium.org/2462973003/ )

Reason for revert:
Causes performance regressions (up to 10% on the "IC" bucket). :-(

Original issue's description:
> [ic] Experiment: disable map-specific handler cache.
>
> IC data handlers support most of the hot cases nowdays. Let's see if
> the map-specific code cache still help us to improve things.
>
> BUG=v8:5561

TBR=ishell@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=v8:5561

Review-Url: https://codereview.chromium.org/2474653002
Cr-Commit-Position: refs/heads/master@{#40701}

src/ic/handler-compiler.cc

@@ -18,9 +18,6 @@ Handle<Code> PropertyHandlerCompiler::Find(Handle<Name> name,
                                            Handle<Map> stub_holder,
                                            Code::Kind kind,
                                            CacheHolderFlag cache_holder) {
-  // TODO(ishell): Experiment: don't cache handlers in map-specific code cache.
-  return Handle<Code>();
-
   Code::Flags flags = Code::ComputeHandlerFlags(kind, cache_holder);
   Code* code = stub_holder->LookupInCodeCache(*name, flags);
   if (code == nullptr) return Handle<Code>();

src/objects.cc

@@ -9992,8 +9992,6 @@ class CodeCache : public AllStatic {
 void Map::UpdateCodeCache(Handle<Map> map,
                           Handle<Name> name,
                           Handle<Code> code) {
-  // TODO(ishell): Experiment: don't cache handlers in map-specific code cache.
-  return;
   Isolate* isolate = map->GetIsolate();
   Handle<FixedArray> cache(map->code_cache(), isolate);
   Handle<FixedArray> new_cache = CodeCache::Put(isolate, cache, name, code);

test/cctest/test-code-cache.cc

@@ -40,9 +40,6 @@ static Handle<Code> GetDummyCode(Isolate* isolate) {
 }  // namespace
 
 TEST(CodeCache) {
-  // TODO(ishell): Experiment: don't cache handlers in map-specific code cache.
-  return;
-
   CcTest::InitializeVM();
   Isolate* isolate = CcTest::i_isolate();
   Factory* factory = isolate->factory();