Support idle time in CPU profiler

src/isolate.h

Index: src/isolate.h
diff --git a/src/isolate.h b/src/isolate.h
index 97291ce5c54cb3fa9e5939166ae1691a3f04f2ff..401505afddaa69b538dba5ded61b2b8438db3ab6 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -661,9 +661,9 @@ class Isolate {
   }
   inline Address* handler_address() { return &thread_local_top_.handler_; }
 
-  // Bottom JS entry (see StackTracer::Trace in sampler.cc).
-  static Address js_entry_sp(ThreadLocalTop* thread) {
-    return thread->js_entry_sp_;
+  // Bottom JS entry.
+  Address js_entry_sp() {
+    return thread_local_top_.js_entry_sp_;
   }
   inline Address* js_entry_sp_address() {
     return &thread_local_top_.js_entry_sp_;