Privately expose DefaultCPUExecutor as a form of InlineExecutor

Summary: DefaultCPUExecutor is the same as InlineExecutor, but hidden to avoid instantiating it to allow filtering on type, primarily in coro::task.

Reviewed By: mpark, terrelln

Differential Revision: D26077566

fbshipit-source-id: 06704134f2446727cbb9f093df0b1954b46d2e49

folly/executors/GlobalExecutor.cpp

@@ -138,6 +138,9 @@ namespace detail {
 std::shared_ptr<Executor> tryGetImmutableCPUPtr() {
   return getImmutable<Executor>();
 }
+bool isDefaultExecutor(Executor* ex) {
+  return dynamic_cast<DefaultCPUExecutor*>(ex);
+}
 } // namespace detail
 
 Executor::KeepAlive<> getGlobalCPUExecutor() {

folly/executors/GlobalExecutor.h

@@ -25,7 +25,8 @@ namespace folly {
 
 namespace detail {
 std::shared_ptr<Executor> tryGetImmutableCPUPtr();
-}
+bool isDefaultExecutor(Executor*);
+} // namespace detail
 
 /**
  * Return the global executor.