Fixes shutdown crashes.

runtime/vm/debugger.cc

Index: runtime/vm/debugger.cc
diff --git a/runtime/vm/debugger.cc b/runtime/vm/debugger.cc
index e8e8af4633b2c7ee8887e86703530d4a1c989d4d..5ed19b4dba26841dfd00fed92e3fc908d67b9d85 100644
--- a/runtime/vm/debugger.cc
+++ b/runtime/vm/debugger.cc
@@ -1277,6 +1277,12 @@ Debugger::~Debugger() {
 
 
 void Debugger::Shutdown() {
+  // TODO(johnmccutchan): Do not create a debugger for isolates that don't need
+  // them. Then, assert here that isolate_ is not one of those isolates.
+  if ((isolate_ == Dart::vm_isolate()) ||
+      ServiceIsolate::IsServiceIsolateDescendant(isolate_)) {
+    return;
+  }
   while (breakpoint_locations_ != NULL) {
     BreakpointLocation* bpt = breakpoint_locations_;
     breakpoint_locations_ = breakpoint_locations_->next();
@@ -1294,9 +1300,7 @@ void Debugger::Shutdown() {
     delete bpt;
   }
   // Signal isolate shutdown event.
-  if (!ServiceIsolate::IsServiceIsolateDescendant(isolate_)) {
-    SignalIsolateEvent(DebuggerEvent::kIsolateShutdown);
-  }
+  SignalIsolateEvent(DebuggerEvent::kIsolateShutdown);
 }