Fix auto suspension of the sampler thread.

src/isolate.h

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 879 matching lines @@
   }
 #endif
 
 #ifdef ENABLE_VMSTATE_TRACKING
   StateTag current_vm_state() {
     return thread_local_top_.current_vm_state_;
   }
 
   void SetCurrentVMState(StateTag state) {
     if (RuntimeProfiler::IsEnabled()) {
-      if (state == JS) {
-        // JS or non-JS -> JS transition.
+      StateTag current_state = thread_local_top_.current_vm_state_;
+      if (current_state != JS && state == JS) {
+        // Non-JS -> JS transition.
         RuntimeProfiler::IsolateEnteredJS(this);
-      } else if (thread_local_top_.current_vm_state_ == JS) {
+      } else if (current_state == JS && state != JS) {
         // JS -> non-JS transition.
         ASSERT(RuntimeProfiler::IsSomeIsolateInJS());
         RuntimeProfiler::IsolateExitedJS(this);
+      } else {
+        // Other types of state transitions are not interesting to the
+        // runtime profiler, because they don't affect whether we're
+        // in JS or not.
+        ASSERT((current_state == JS) == (state == JS));
       }
     }
     thread_local_top_.current_vm_state_ = state;
   }
 #endif
 
   void ResetEagerOptimizingData();
 
  private:
   Isolate();
@@ skipping 380 matching lines @@
 
 } }  // namespace v8::internal
 
 // TODO(isolates): Get rid of these -inl.h includes and place them only where
 //                 they're needed.
 #include "allocation-inl.h"
 #include "zone-inl.h"
 #include "frames-inl.h"
 
 #endif  // V8_ISOLATE_H_