[cleanup] Store ES6 class' start/end positions as one property.

... containing Tuple2 value instead of two properties. This CL reduces the
number of property queries in FunctionToString to one and it is memory-neutral.

Change-Id: Ia6fa267f3e5b6670013f1da3e03cd70bf24dd65a
Reviewed-on: https://chromium-review.googlesource.com/730744Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48926}

src/heap-symbols.h

@@ -214,8 +214,7 @@
   V(call_site_frame_index_symbol)           \
   V(console_context_id_symbol)              \
   V(console_context_name_symbol)            \
-  V(class_end_position_symbol)              \
-  V(class_start_position_symbol)            \
+  V(class_positions_symbol)                 \
   V(detailed_stack_trace_symbol)            \
   V(elements_transition_symbol)             \
   V(error_end_pos_symbol)                   \

src/objects.cc

@@ -13118,16 +13118,16 @@ Handle<String> JSFunction::ToString(Handle<JSFunction> function) {
   }
 
   // Check if we should print {function} as a class.
-  Handle<Object> class_start_position = JSReceiver::GetDataProperty(
-      function, isolate->factory()->class_start_position_symbol());
-  if (class_start_position->IsSmi()) {
-    Handle<Object> class_end_position = JSReceiver::GetDataProperty(
-        function, isolate->factory()->class_end_position_symbol());
+  Handle<Object> maybe_class_positions = JSReceiver::GetDataProperty(
+      function, isolate->factory()->class_positions_symbol());
+  if (maybe_class_positions->IsTuple2()) {
+    Tuple2* class_positions = Tuple2::cast(*maybe_class_positions);
+    int start_position = Smi::ToInt(class_positions->value1());
+    int end_position = Smi::ToInt(class_positions->value2());
     Handle<String> script_source(
         String::cast(Script::cast(shared_info->script())->source()), isolate);
-    return isolate->factory()->NewSubString(
-        script_source, Handle<Smi>::cast(class_start_position)->value(),
-        Handle<Smi>::cast(class_end_position)->value());
+    return isolate->factory()->NewSubString(script_source, start_position,
+                                            end_position);
   }
 
   // Check if we have source code for the {function}.

src/runtime/runtime-classes.cc

@@ -166,18 +166,18 @@ static MaybeHandle<Object> DefineClass(Isolate* isolate,
                         constructor, DONT_ENUM);
 
   // Install private properties that are used to construct the FunctionToString.
-  RETURN_ON_EXCEPTION(
-      isolate,
-      Object::SetProperty(
-          constructor, isolate->factory()->class_start_position_symbol(),
-          handle(Smi::FromInt(start_position), isolate), LanguageMode::kStrict),
-      Object);
-  RETURN_ON_EXCEPTION(
-      isolate,
-      Object::SetProperty(
-          constructor, isolate->factory()->class_end_position_symbol(),
-          handle(Smi::FromInt(end_position), isolate), LanguageMode::kStrict),
-      Object);
+  {
+    Handle<Smi> start(Smi::FromInt(start_position), isolate);
+    Handle<Smi> end(Smi::FromInt(end_position), isolate);
+    Handle<Tuple2> class_positions =
+        isolate->factory()->NewTuple2(start, end, NOT_TENURED);
+    RETURN_ON_EXCEPTION(
+        isolate,
+        Object::SetProperty(constructor,
+                            isolate->factory()->class_positions_symbol(),
+                            class_positions, LanguageMode::kStrict),
+        Object);
+  }
 
   // Caller already has access to constructor, so return the prototype.
   return prototype;