Refactor isolate interrupts to use OOB messages instead of interrupt bits.

runtime/vm/service.cc

Index: runtime/vm/service.cc
diff --git a/runtime/vm/service.cc b/runtime/vm/service.cc
index 4cb379eeb177e48843c5bef39274597f6054cc35..1dc403b15ffc2cfc67d5c998bb0dd50447365932 100644
--- a/runtime/vm/service.cc
+++ b/runtime/vm/service.cc
@@ -2423,8 +2423,12 @@ static const MethodParameter* pause_params[] = {
 
 
 static bool Pause(Isolate* isolate, JSONStream* js) {
-  // TODO(turnidge): Don't double-interrupt the isolate here.
-  isolate->ScheduleInterrupts(Isolate::kApiInterrupt);
+  // TODO(turnidge): This interrupt message could have been sent from
+  // the service isolate directly, but would require some special case
+  // code.  That would prevent this isolate getting double-interrupted
+  // with OOB messages.
+  isolate->SendInternalLibMessage(Isolate::kInterruptMsg,
+                                  isolate->pause_capability());
   PrintSuccess(js);
   return true;
 }