Stop profiler on isolate teardown if still running

If the profiler is started via the API and not stopped, V8 will
 intermittently crash during isolate teardown.

The fix is to run the DeleteAllProfiles function in Isolate::Deinit()
 if cpu_profiler_ still exists.

https://groups.google.com/forum/#!topic/v8-dev/WsIlpbaD4mo

TEST= Run in debug mode, if you start a profile and don't stop it,
 this assert should fail:

  Fatal error in ../src/profiler/cpu-profiler.cc, line 414
  Check failed: !is_profiling_.

Review URL: https://codereview.chromium.org/1526253005

Cr-Commit-Position: refs/heads/master@{#32953}

src/isolate.cc

@@ -1895,6 +1895,10 @@ void Isolate::Deinit() {
     PrintF(stdout, "=== Stress deopt counter: %u\n", stress_deopt_count_);
   }
 
+  if (cpu_profiler_) {
+    cpu_profiler_->DeleteAllProfiles();
+  }
+
   // We must stop the logger before we tear down other components.
   Sampler* sampler = logger_->sampler();
   if (sampler && sampler->IsActive()) sampler->Stop();