Use background tasks for the compiler dispatcher

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

Index: test/unittests/compiler-dispatcher/compiler-dispatcher-unittest.cc
diff --git a/test/unittests/compiler-dispatcher/compiler-dispatcher-unittest.cc b/test/unittests/compiler-dispatcher/compiler-dispatcher-unittest.cc
index ae176408fdf47e02106ed5bea7f95e778b8c0734..8f1f9e8e7a1aa96240525b56f2969ccf0b66b133 100644
--- a/test/unittests/compiler-dispatcher/compiler-dispatcher-unittest.cc
+++ b/test/unittests/compiler-dispatcher/compiler-dispatcher-unittest.cc
@@ -47,6 +47,8 @@ class MockPlatform : public v8::Platform {
   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();