Simplify and correctify pending message location handling.

This makes sure that the pending message location is only tracked by
the message object, as only this is saved for finally-blocks. The
location information is duplicated and becomes stale.

R=titzer@chromium.org
TEST=maeh, not so much.

Review URL: https://codereview.chromium.org/987353002

Cr-Commit-Position: refs/heads/master@{#27109}

include/v8.h

@@ -6089,8 +6089,6 @@ class V8_EXPORT TryCatch {
   void* message_obj_;
   void* message_script_;
   void* js_stack_comparable_address_;
-  int message_start_pos_;
-  int message_end_pos_;
   bool is_verbose_ : 1;
   bool can_continue_ : 1;
   bool capture_message_ : 1;

src/api.cc

@@ -2144,8 +2144,6 @@ void v8::TryCatch::ResetInternal() {
   exception_ = the_hole;
   message_obj_ = the_hole;
   message_script_ = the_hole;
-  message_start_pos_ = 0;
-  message_end_pos_ = 0;
 }
 
 

src/isolate.cc

@@ -990,8 +990,6 @@ Object* Isolate::Throw(Object* exception, MessageLocation* location) {
 
       thread_local_top()->pending_message_obj_ = *message_obj;
       thread_local_top()->pending_message_script_ = *location->script();
-      thread_local_top()->pending_message_start_pos_ = location->start_pos();
-      thread_local_top()->pending_message_end_pos_ = location->end_pos();
 
       // If the abort-on-uncaught-exception flag is specified, abort on any
       // exception not caught by JavaScript, even when an external handler is
@@ -1168,8 +1166,6 @@ void Isolate::RestorePendingMessageFromTryCatch(v8::TryCatch* handler) {
   DCHECK(script->IsScript() || script->IsTheHole());
   thread_local_top()->pending_message_obj_ = message;
   thread_local_top()->pending_message_script_ = script;
-  thread_local_top()->pending_message_start_pos_ = handler->message_start_pos_;
-  thread_local_top()->pending_message_end_pos_ = handler->message_end_pos_;
 }
 
 
@@ -1448,13 +1444,13 @@ void Isolate::ReportPendingMessages() {
       thread_local_top_.has_pending_message_ = false;
       if (!thread_local_top_.pending_message_obj_->IsTheHole()) {
         HandleScope scope(this);
-        Handle<Object> message_obj(thread_local_top_.pending_message_obj_,
-                                   this);
+        Handle<JSMessageObject> message_obj(
+            JSMessageObject::cast(thread_local_top_.pending_message_obj_));
         if (!thread_local_top_.pending_message_script_->IsTheHole()) {
           Handle<Script> script(
               Script::cast(thread_local_top_.pending_message_script_));
-          int start_pos = thread_local_top_.pending_message_start_pos_;
-          int end_pos = thread_local_top_.pending_message_end_pos_;
+          int start_pos = message_obj->start_position();
+          int end_pos = message_obj->end_position();
           MessageLocation location(script, start_pos, end_pos);
           MessageHandler::ReportMessage(this, &location, message_obj);
         } else {
@@ -1473,10 +1469,12 @@ MessageLocation Isolate::GetMessageLocation() {
   if (thread_local_top_.pending_exception_ != heap()->termination_exception() &&
       thread_local_top_.has_pending_message_ &&
       !thread_local_top_.pending_message_obj_->IsTheHole()) {
+    Handle<JSMessageObject> message_obj(
+        JSMessageObject::cast(thread_local_top_.pending_message_obj_));
     Handle<Script> script(
         Script::cast(thread_local_top_.pending_message_script_));
-    int start_pos = thread_local_top_.pending_message_start_pos_;
-    int end_pos = thread_local_top_.pending_message_end_pos_;
+    int start_pos = message_obj->start_position();
+    int end_pos = message_obj->end_position();
     return MessageLocation(script, start_pos, end_pos);
   }
 
@@ -2000,8 +1998,6 @@ bool Isolate::PropagatePendingExceptionToExternalTryCatch() {
 
     handler->message_obj_ = thread_local_top_.pending_message_obj_;
     handler->message_script_ = thread_local_top_.pending_message_script_;
-    handler->message_start_pos_ = thread_local_top_.pending_message_start_pos_;
-    handler->message_end_pos_ = thread_local_top_.pending_message_end_pos_;
   }
   return true;
 }

src/isolate.h

@@ -286,8 +286,6 @@ class ThreadLocalTop BASE_EMBEDDED {
   bool rethrowing_message_;
   Object* pending_message_obj_;
   Object* pending_message_script_;
-  int pending_message_start_pos_;
-  int pending_message_end_pos_;
 
   // Use a separate value for scheduled exceptions to preserve the
   // invariants that hold about pending_exception.  We may want to