Fix use of history timers in background threads.

src/isolate.h

Index: src/isolate.h
diff --git a/src/isolate.h b/src/isolate.h
index 66af826b5bb8e169f86d84f5e41a5ce068f50f0f..1ad4a640d3ea52132e484a1b2cc407d0069c2a05 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -871,13 +871,20 @@ class Isolate {
 #undef NATIVE_CONTEXT_FIELD_ACCESSOR
 
   Bootstrapper* bootstrapper() { return bootstrapper_; }
+  // Use for updating counters on a foreground thread.
   Counters* counters() {
-    // Call InitializeLoggingAndCounters() if logging is needed before
-    // the isolate is fully initialized.
+    DCHECK(!IsIsolateInBackground());
+    // Make sure InitializeCounters() has been called.
     DCHECK_NOT_NULL(counters_shared_.get());
     return counters_shared_.get();
   }
-  std::shared_ptr<Counters> counters_shared() { return counters_shared_; }
+  // Use for updating counters on a background thread.
+  std::shared_ptr<Counters> counters_shared() {

[Mircea Trofin, 2017/06/22 18:42:24]

nit: shared_counters?

[kschimpf, 2017/06/22 20:38:31]

Actually, to make clear it's context, I'll rename it to async_counters().

+    DCHECK(!IsIsolateInBackground());
+    // Make sure InitializeCounters() has been called.
+    DCHECK_NOT_NULL(counters_shared_.get());
+    return counters_shared_;
+  }
   RuntimeProfiler* runtime_profiler() { return runtime_profiler_; }
   CompilationCache* compilation_cache() { return compilation_cache_; }
   Logger* logger() {