Fixes crashes in VM isolate shutdown.

runtime/vm/debugger_api_impl.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "include/dart_debugger_api.h"
 
 #include "vm/class_finalizer.h"
 #include "vm/compiler.h"
 #include "vm/dart_api_impl.h"
 #include "vm/dart_api_state.h"
@@ skipping 92 matching lines @@
 
 static Dart_PausedEventHandler* paused_event_handler = NULL;
 static Dart_BreakpointResolvedHandler* bp_resolved_handler = NULL;
 static Dart_ExceptionThrownHandler* exc_thrown_handler = NULL;
 static Dart_IsolateEventHandler* isolate_event_handler = NULL;
 
 
 static void DebuggerEventHandler(DebuggerEvent* event) {
   Isolate* isolate = Isolate::Current();
   ASSERT(isolate != NULL);
-  ASSERT(isolate->debugger() != NULL);
   Dart_EnterScope();
   Dart_IsolateId isolate_id = isolate->debugger()->GetIsolateId();
   if (event->type() == DebuggerEvent::kBreakpointReached) {
     if (paused_event_handler != NULL) {
       Dart_CodeLocation location;
       ActivationFrame* top_frame = event->top_frame();
       location.script_url = Api::NewHandle(isolate, top_frame->SourceUrl());
       const Library& lib = Library::Handle(top_frame->Library());
       location.library_id = lib.index();
       location.token_pos = top_frame->TokenPos();
@@ skipping 209 matching lines @@
 
 
 DART_EXPORT Dart_Handle Dart_SetBreakpoint(
                             Dart_Handle script_url_in,
                             intptr_t line_number) {
   Isolate* isolate = Isolate::Current();
   DARTSCOPE(isolate);
   UNWRAP_AND_CHECK_PARAM(String, script_url, script_url_in);
 
   Debugger* debugger = isolate->debugger();
-  ASSERT(debugger != NULL);
   Breakpoint* bpt =
       debugger->SetBreakpointAtLine(script_url, line_number);
   if (bpt == NULL) {
     return Api::NewError("%s: could not set breakpoint at line %" Pd " in '%s'",
                          CURRENT_FUNC, line_number, script_url.ToCString());
   }
   return Dart_NewInteger(bpt->id());
 }
 
 
 DART_EXPORT Dart_Handle Dart_GetBreakpointURL(intptr_t bp_id) {
   Isolate* isolate = Isolate::Current();
   DARTSCOPE(isolate);
   Debugger* debugger = isolate->debugger();
-  ASSERT(debugger != NULL);
 
   Breakpoint* bpt = debugger->GetBreakpointById(bp_id);
   if (bpt == NULL) {
     return Api::NewError("%s: breakpoint with id %" Pd " does not exist",
                            CURRENT_FUNC, bp_id);
   }
   return Api::NewHandle(isolate, bpt->bpt_location()->url());
 }
 
 
 DART_EXPORT Dart_Handle Dart_GetBreakpointLine(intptr_t bp_id) {
   Isolate* isolate = Isolate::Current();
   DARTSCOPE(isolate);
   Debugger* debugger = isolate->debugger();
-  ASSERT(debugger != NULL);
 
   Breakpoint* bpt = debugger->GetBreakpointById(bp_id);
   if (bpt == NULL) {
     return Api::NewError("%s: breakpoint with id %" Pd " does not exist",
                          CURRENT_FUNC, bp_id);
   }
   return Dart_NewInteger(bpt->bpt_location()->LineNumber());
 }
 
 
@@ skipping 72 matching lines @@
   if (!error.IsNull()) {
     return Api::NewHandle(isolate, error.raw());
   }
   return Api::Success();
 }
 
 
 DART_EXPORT Dart_Handle Dart_RemoveBreakpoint(intptr_t bp_id) {
   Isolate* isolate = Isolate::Current();
   DARTSCOPE(isolate);
-  Debugger* debugger = isolate->debugger();
-  ASSERT(debugger != NULL);
-
   isolate->debugger()->RemoveBreakpoint(bp_id);
   return Api::Success();
 }
 
 
 DART_EXPORT Dart_Handle Dart_SetStepOver() {
   Isolate* isolate = Isolate::Current();
   DARTSCOPE(isolate);
   isolate->debugger()->SetStepOver();
   return Api::Success();
@@ skipping 501 matching lines @@
   return Api::CastIsolate(isolate);
 }
 
 
 DART_EXPORT Dart_IsolateId Dart_GetIsolateId(Dart_Isolate dart_isolate) {
   Isolate* isolate = reinterpret_cast<Isolate*>(dart_isolate);
   return isolate->debugger()->GetIsolateId();
 }
 
 }  // namespace dart