Remove superfluous ThreadLocalTop::catcher field.

The external v8::TryCatch handler was computed eagerly and kept in
intact. This changes it to be computed lazily for simplicity and
readability of the code.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/997863003

Cr-Commit-Position: refs/heads/master@{#27132}

src/isolate.cc

@@ -82,7 +82,6 @@ void ThreadLocalTop::InitializeInternal() {
   external_caught_exception_ = false;
   failed_access_check_callback_ = NULL;
   save_context_ = NULL;
-  catcher_ = NULL;
   promise_on_stack_ = NULL;
 
   // These members are re-initialized later after deserialization
@@ -252,7 +251,6 @@ void Isolate::RegisterTryCatchHandler(v8::TryCatch* that) {
 void Isolate::UnregisterTryCatchHandler(v8::TryCatch* that) {
   DCHECK(thread_local_top()->try_catch_handler() == that);
   thread_local_top()->set_try_catch_handler(that->next_);
-  thread_local_top()->catcher_ = NULL;
 }
 
 
@@ -1005,11 +1003,6 @@ Object* Isolate::Throw(Object* exception, MessageLocation* location) {
   // Save the message for reporting if the the exception remains uncaught.
   thread_local_top()->has_pending_message_ = report_exception;
 
-  // Do not forget to clean catcher_ if currently thrown exception cannot
-  // be caught.  If necessary, ReThrow will update the catcher.
-  thread_local_top()->catcher_ =
-      can_be_caught_externally ? try_catch_handler() : NULL;
-
   // Set the exception being thrown.
   set_pending_exception(*exception_handle);
   return heap()->exception();
@@ -1017,12 +1010,7 @@ Object* Isolate::Throw(Object* exception, MessageLocation* location) {
 
 
 Object* Isolate::ReThrow(Object* exception) {
-  bool can_be_caught_externally = false;
-  bool catchable_by_javascript = is_catchable_by_javascript(exception);
-  ShouldReportException(&can_be_caught_externally, catchable_by_javascript);
-
-  thread_local_top()->catcher_ = can_be_caught_externally ?
-      try_catch_handler() : NULL;
+  DCHECK(!has_pending_exception());
 
   // Set the exception being re-thrown.
   set_pending_exception(exception);
@@ -1387,14 +1375,6 @@ Handle<JSMessageObject> Isolate::CreateMessage(Handle<Object> exception,
 }
 
 
-bool Isolate::HasExternalTryCatch() {
-  DCHECK(has_pending_exception());
-
-  return (thread_local_top()->catcher_ != NULL) &&
-      (try_catch_handler() == thread_local_top()->catcher_);
-}
-
-
 bool Isolate::IsFinallyOnTop() {
   // Get the address of the external handler so we can compare the address to
   // determine which one is closer to the top of the stack.
@@ -1954,22 +1934,23 @@ void Isolate::InitializeThreadLocal() {
 
 
 bool Isolate::PropagatePendingExceptionToExternalTryCatch() {
-  DCHECK(has_pending_exception());
+  Object* exception = pending_exception();
 
-  bool has_external_try_catch = HasExternalTryCatch();
-  if (!has_external_try_catch) {
+  bool can_be_caught_externally = false;
+  bool catchable_by_javascript = is_catchable_by_javascript(exception);
+  ShouldReportException(&can_be_caught_externally, catchable_by_javascript);
+  if (!can_be_caught_externally) {
     thread_local_top_.external_caught_exception_ = false;
     return true;
   }
 
-  bool catchable_by_js = is_catchable_by_javascript(pending_exception());
-  if (catchable_by_js && IsFinallyOnTop()) {
+  if (catchable_by_javascript && IsFinallyOnTop()) {
     thread_local_top_.external_caught_exception_ = false;
     return false;
   }
 
   thread_local_top_.external_caught_exception_ = true;
-  if (thread_local_top_.pending_exception_ == heap()->termination_exception()) {
+  if (!catchable_by_javascript) {
     try_catch_handler()->can_continue_ = false;
     try_catch_handler()->has_terminated_ = true;
     try_catch_handler()->exception_ = heap()->null_value();

src/isolate.h

@@ -292,7 +292,6 @@ class ThreadLocalTop BASE_EMBEDDED {
   Object* scheduled_exception_;
   bool external_caught_exception_;
   SaveContext* save_context_;
-  v8::TryCatch* catcher_;
 
   // Stack.
   Address c_entry_fp_;  // the frame pointer of the top c entry frame
@@ -618,8 +617,6 @@ class Isolate {
     return &thread_local_top_.external_caught_exception_;
   }
 
-  THREAD_LOCAL_TOP_ACCESSOR(v8::TryCatch*, catcher)
-
   THREAD_LOCAL_TOP_ADDRESS(Object*, scheduled_exception)
 
   Address pending_message_obj_address() {
@@ -644,7 +641,6 @@ class Isolate {
     thread_local_top_.scheduled_exception_ = heap_.the_hole_value();
   }
 
-  bool HasExternalTryCatch();
   bool IsFinallyOnTop();
 
   bool is_catchable_by_javascript(Object* exception) {
@@ -708,23 +704,19 @@ class Isolate {
 
   class ExceptionScope {
    public:
-    explicit ExceptionScope(Isolate* isolate) :
-      // Scope currently can only be used for regular exceptions,
-      // not termination exception.
-      isolate_(isolate),
-      pending_exception_(isolate_->pending_exception(), isolate_),
-      catcher_(isolate_->catcher())
-    { }
+    // Scope currently can only be used for regular exceptions,
+    // not termination exception.
+    explicit ExceptionScope(Isolate* isolate)
+        : isolate_(isolate),
+          pending_exception_(isolate_->pending_exception(), isolate_) {}
 
     ~ExceptionScope() {
-      isolate_->set_catcher(catcher_);
       isolate_->set_pending_exception(*pending_exception_);
     }
 
    private:
     Isolate* isolate_;
     Handle<Object> pending_exception_;
-    v8::TryCatch* catcher_;
   };
 
   void SetCaptureStackTraceForUncaughtExceptions(