[wasm] Remove dead code

Background task restarting happens now in the CompilationState and not
in the AsyncCompileJob. The code in the AsyncCompileJob is dead, so I
remove it.

R=titzer@chromium.org

Change-Id: Ife52522a00ec43aa0f9ad50f8e0114c1e4da5db7
Reviewed-on: https://chromium-review.googlesource.com/978322Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52190}

src/wasm/module-compiler.cc

@@ -2918,15 +2918,6 @@ void AsyncCompileJob::StartBackgroundTask() {
       base::make_unique<CompileTask>(this, false));
 }
 
-void AsyncCompileJob::RestartBackgroundTasks() {
-  int num_restarts = stopped_tasks_.Value();
-  stopped_tasks_.Decrement(num_restarts);
-
-  for (int i = 0; i < num_restarts; ++i) {
-    StartBackgroundTask();
-  }
-}
-
 template <typename Step, typename... Args>
 void AsyncCompileJob::DoAsync(Args&&... args) {
   NextStep<Step>(std::forward<Args>(args)...);

src/wasm/module-compiler.h

@@ -151,8 +151,6 @@ class AsyncCompileJob {
 
   void StartBackgroundTask();
 
-  void RestartBackgroundTasks();
-
   // Switches to the compilation step {Step} and starts a foreground task to
   // execute it.
   template <typename Step, typename... Args>
@@ -191,8 +189,6 @@ class AsyncCompileJob {
 
   std::shared_ptr<v8::TaskRunner> foreground_task_runner_;
   std::shared_ptr<v8::TaskRunner> background_task_runner_;
-  // The number of background tasks which stopped executing within a step.
-  base::AtomicNumber<int32_t> stopped_tasks_{0};
 
   // For async compilation the AsyncCompileJob is the only finisher. For
   // streaming compilation also the AsyncStreamingProcessor has to finish before