v8: backport pieces of dab18fb0bbcdd

Backport ABI-incompatible changes from
dab18fb0bbcdd (“Make idle tasks optional in the default platform.”).

Ref: https://codereview.chromium.org/2737743002
Ref: https://github.com/v8/v8/commit/dab18fb0bbcdd

PR-URL: https://github.com/nodejs/node/pull/12875
Reviewed-By: James M Snell <jasnell@gmail.com>

deps/v8/include/libplatform/libplatform.h

@@ -12,6 +12,8 @@
 namespace v8 {
 namespace platform {
 
+enum class IdleTaskSupport { kDisabled, kEnabled };
+
 /**
  * Returns a new instance of the default v8::Platform implementation.
  *
@@ -21,7 +23,8 @@ namespace platform {
  * processors online will be chosen.
  */
 V8_PLATFORM_EXPORT v8::Platform* CreateDefaultPlatform(
-    int thread_pool_size = 0);
+    int thread_pool_size = 0,
+    IdleTaskSupport idle_task_support = IdleTaskSupport::kDisabled);
 
 /**
  * Pumps the message loop for the given isolate.

deps/v8/src/libplatform/default-platform.cc

@@ -17,8 +17,8 @@
 namespace v8 {
 namespace platform {
 
-
-v8::Platform* CreateDefaultPlatform(int thread_pool_size) {
+v8::Platform* CreateDefaultPlatform(int thread_pool_size,
+                                    IdleTaskSupport idle_task_support) {
   DefaultPlatform* platform = new DefaultPlatform();
   platform->SetThreadPoolSize(thread_pool_size);
   platform->EnsureInitialized();