[wasm] No foreground tasks in compilation state

This removes the last creation of foreground tasks in the compilation
state. I think this logic can be removed completely, because
a) the number of background tasks is already capped at {max(1,
   FLAG_wasm_num_compilation_tasks)}, and
b) in order to get predictable timing you can use the --predictable
   flag which makes all background tasks execute synchronously with
   foreground tasks (from the same queue).

R=ahaas@chromium.org
CC=mstarzinger@chromium.org

Bug: v8:8050, v8:8689
Change-Id: I142af6b42f9bb9befc7c7b7d6002192d72bd7677
Reviewed-on: https://chromium-review.googlesource.com/c/1451841
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59341}

src/wasm/module-compiler.cc

@@ -257,9 +257,6 @@ class CompilationStateImpl {
   // the foreground thread.
   std::vector<CompilationState::callback_t> callbacks_;
 
-  CancelableTaskManager foreground_task_manager_;
-  std::shared_ptr<v8::TaskRunner> foreground_task_runner_;
-
   const size_t max_background_tasks_ = 0;
 };
 
@@ -1477,21 +1474,15 @@ CompilationStateImpl::CompilationStateImpl(
       async_counters_(std::move(async_counters)),
       max_background_tasks_(std::max(
           1, std::min(FLAG_wasm_num_compilation_tasks,
-                      V8::GetCurrentPlatform()->NumberOfWorkerThreads()))) {
-  v8::Isolate* v8_isolate = reinterpret_cast<v8::Isolate*>(isolate_);
-  v8::Platform* platform = V8::GetCurrentPlatform();
-  foreground_task_runner_ = platform->GetForegroundTaskRunner(v8_isolate);
-}
+                      V8::GetCurrentPlatform()->NumberOfWorkerThreads()))) {}
 
 CompilationStateImpl::~CompilationStateImpl() {
-  DCHECK(foreground_task_manager_.canceled());
   CompilationError* error = compile_error_.load(std::memory_order_acquire);
   if (error != nullptr) delete error;
 }
 
 void CompilationStateImpl::AbortCompilation() {
   Abort();
-  foreground_task_manager_.CancelAndWait();
 }
 
 void CompilationStateImpl::SetNumberOfFunctionsToCompile(size_t num_functions) {
@@ -1596,13 +1587,6 @@ void CompilationStateImpl::RestartBackgroundCompileTask() {
   auto task = engine_->NewBackgroundCompileTask<BackgroundCompileTask>(
       background_compile_token_, async_counters_);
 
-  // If --wasm-num-compilation-tasks=0 is passed, do only spawn foreground
-  // tasks. This is used to make timing deterministic.
-  if (FLAG_wasm_num_compilation_tasks == 0) {
-    foreground_task_runner_->PostTask(std::move(task));
-    return;
-  }
-
   if (baseline_compilation_finished()) {
     V8::GetCurrentPlatform()->CallLowPriorityTaskOnWorkerThread(
         std::move(task));