Reduce CPU usage when no isolates need to be profiled.

runtime/vm/isolate.cc

 // Copyright (c) 2013, 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 "vm/isolate.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/json.h"
 #include "lib/mirrors.h"
@@ skipping 986 matching lines @@
   }
   {
     JSONArray features_array(&jsobj, "features");
     if (is_io_enabled) {
       features_array.AddValue("io");
     }
   }
 }
 
 
-void Isolate::ProfileInterrupt() {
+intptr_t Isolate::ProfileInterrupt() {
+  if (profiler_data() == NULL) {
+    // Profiler not setup for isolate.
+    return 0;
+  }
+  if (profiler_data()->blocked()) {
+    // Profiler blocked for this isolate.
+    return 0;
+  }
   InterruptableThreadState* state = thread_state();
   if (state == NULL) {
     // Isolate is not scheduled on a thread.
     ProfileIdle();
-    return;
+    return 1;
   }
   ASSERT(state->id != Thread::kInvalidThreadId);
   ThreadInterrupter::InterruptThread(state);
+  return 1;
 }
 
 
 void Isolate::ProfileIdle() {
   vm_tag_counters_.Increment(vm_tag());
 }
 
 
 void Isolate::set_tag_table(const GrowableObjectArray& value) {
   tag_table_ = value.raw();
@@ skipping 169 matching lines @@
   return func.raw();
 }
 
 
 void IsolateSpawnState::Cleanup() {
   SwitchIsolateScope switch_scope(isolate());
   Dart::ShutdownIsolate();
 }
 
 }  // namespace dart