Use background tasks for the compiler dispatcher

test/unittests/compiler-dispatcher/compiler-dispatcher-unittest.cc

 // Copyright 2016 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/compiler-dispatcher/compiler-dispatcher.h"
 
 #include "include/v8-platform.h"
 #include "src/compiler-dispatcher/compiler-dispatcher-job.h"
 #include "src/flags.h"
 #include "src/handles.h"
@@ skipping 29 matching lines @@
 
 bool CompilerDispatcherTest::old_flag_;
 
 namespace {
 
 class MockPlatform : public v8::Platform {
  public:
   MockPlatform() : task_(nullptr), time_(0.0), time_step_(0.0) {}
   ~MockPlatform() override = default;
 
+  size_t NumberOfAvailableBackgroundThreads() override { return 1; }
+
   void CallOnBackgroundThread(Task* task,
                               ExpectedRuntime expected_runtime) override {
     UNREACHABLE();
   }
 
   void CallOnForegroundThread(v8::Isolate* isolate, Task* task) override {
     UNREACHABLE();
   }
 
   void CallDelayedOnForegroundThread(v8::Isolate* isolate, Task* task,
@@ skipping 160 matching lines @@
   // to finish compiling the function.
   platform.RunIdleTask(1000.0, 0.0);
 
   ASSERT_FALSE(dispatcher.IsEnqueued(shared));
   ASSERT_FALSE(shared->is_compiled());
   ASSERT_FALSE(try_catch.HasCaught());
 }
 
 }  // namespace internal
 }  // namespace v8