Speed up common ObjectProtoToString cases

1) avoid the builder
2) by precomputing the result we're guaranteed to have a flat string
avoiding extra cost later of using the string

BUG=

Review-Url: https://codereview.chromium.org/1988023004
Cr-Commit-Position: refs/heads/master@{#36352}

src/heap-symbols.h

@@ -12,6 +12,10 @@
   V(arguments_string, "arguments")                                 \
   V(Arguments_string, "Arguments")                                 \
   V(Array_string, "Array")                                         \
+  V(array_to_string, "[object Array]")                             \
+  V(object_to_string, "[object Object]")                           \
+  V(string_to_string, "[object String]")                           \
+  V(function_to_string, "[object Function]")                       \
   V(bind_string, "bind")                                           \
   V(bool16x8_string, "bool16x8")                                   \
   V(Bool16x8_string, "Bool16x8")                                   \

src/objects.cc

@@ -15236,8 +15236,12 @@ bool JSObject::WasConstructedFromApiFunction() {
 
 MaybeHandle<String> Object::ObjectProtoToString(Isolate* isolate,
                                                 Handle<Object> object) {
-  if (object->IsUndefined()) return isolate->factory()->undefined_to_string();
-  if (object->IsNull()) return isolate->factory()->null_to_string();
+  if (*object == isolate->heap()->undefined_value()) {
+    return isolate->factory()->undefined_to_string();
+  }
+  if (*object == isolate->heap()->null_value()) {
+    return isolate->factory()->null_to_string();
+  }
 
   Handle<JSReceiver> receiver =
       Object::ToObject(isolate, object).ToHandleChecked();
@@ -15258,6 +15262,18 @@ MaybeHandle<String> Object::ObjectProtoToString(Isolate* isolate,
                                JSReceiver::BuiltinStringTag(receiver), String);
   }
 
+  if (*tag == isolate->heap()->Object_string()) {
+    return isolate->factory()->object_to_string();
+  }
+  if (*tag == isolate->heap()->String_string()) {
+    return isolate->factory()->string_to_string();
+  }
+  if (*tag == isolate->heap()->Array_string()) {
+    return isolate->factory()->array_to_string();
+  }
+  if (*tag == isolate->heap()->Function_string()) {
+    return isolate->factory()->function_to_string();
+  }
   IncrementalStringBuilder builder(isolate);
   builder.AppendCString("[object ");
   builder.AppendString(tag);