Add --single-threaded flag that disables background threads.

src/optimizing-compiler-thread.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/optimizing-compiler-thread.h"
 
 #include "src/v8.h"
 
 #include "src/base/atomicops.h"
 #include "src/full-codegen.h"
@@ skipping 354 matching lines @@
   } else {
     // Add job to the back of the input queue.
     base::LockGuard<base::Mutex> access_input_queue(&input_queue_mutex_);
     DCHECK_LT(input_queue_length_, input_queue_capacity_);
     input_queue_[InputQueueIndex(input_queue_length_)] = job;
     input_queue_length_++;
   }
   if (FLAG_block_concurrent_recompilation) {
     blocked_jobs_++;
   } else if (job_based_recompilation_) {
+    DCHECK(!FLAG_single_threaded);
     base::LockGuard<base::RecursiveMutex> lock(&task_count_mutex_);
     ++task_count_;
     V8::GetCurrentPlatform()->CallOnBackgroundThread(
         new CompileTask(isolate_), v8::Platform::kShortRunningTask);
   } else {
     input_queue_semaphore_.Signal();
   }
 }
 
 
 void OptimizingCompilerThread::Unblock() {
   DCHECK(!IsOptimizerThread());
   {
     base::LockGuard<base::RecursiveMutex> lock(&task_count_mutex_);
     task_count_ += blocked_jobs_;
   }
   while (blocked_jobs_ > 0) {
     if (job_based_recompilation_) {
+      DCHECK(!FLAG_single_threaded);
       V8::GetCurrentPlatform()->CallOnBackgroundThread(
           new CompileTask(isolate_), v8::Platform::kShortRunningTask);
     } else {
       input_queue_semaphore_.Signal();
     }
     blocked_jobs_--;
   }
 }
 
 
@@ skipping 74 matching lines @@
 
 
 bool OptimizingCompilerThread::IsOptimizerThread() {
   base::LockGuard<base::Mutex> lock_guard(&thread_id_mutex_);
   return ThreadId::Current().ToInteger() == thread_id_;
 }
 #endif
 
 
 } }  // namespace v8::internal