Only resume operations after aborting if all background tasks are done

BUG=v8:6069
R=rmcilroy@chromium.org

Change-Id: I4bd696163f113e166c4be70d6688b17ff5abbcbb
Reviewed-on: https://chromium-review.googlesource.com/455917Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43851}

src/compiler-dispatcher/compiler-dispatcher.cc

@@ -411,7 +411,7 @@ bool CompilerDispatcher::FinishNow(Handle<SharedFunctionInfo> function) {
   jobs_.erase(job);
   if (jobs_.empty()) {
     base::LockGuard<base::Mutex> lock(&mutex_);
-    abort_ = false;
+    if (num_background_tasks_ == 0) abort_ = false;
   }
   return result;
 }
@@ -479,7 +479,7 @@ void CompilerDispatcher::AbortInactiveJobs() {
   }
   if (jobs_.empty()) {
     base::LockGuard<base::Mutex> lock(&mutex_);
-    abort_ = false;
+    if (num_background_tasks_ == 0) abort_ = false;
   }
 }