[platform] Add TaskRunner::PostNonNestableTask

The API will be used to post GC tasks that benefit from being executed
at top level.

Bug: chromium:843903
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: I062855e810ca9a8d8af8ae8b66e02c85e108798b
Reviewed-on: https://chromium-review.googlesource.com/c/1273045Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56528}

include/v8-platform.h

@@ -53,6 +53,15 @@ class TaskRunner {
    */
   virtual void PostTask(std::unique_ptr<Task> task) = 0;
 
+  /**
+   * Schedules a task to be invoked by this TaskRunner. The TaskRunner
+   * implementation takes ownership of |task|. The |task| cannot be nested
+   * within other task executions.
+   *
+   * Requires that |TaskRunner::NonNestableTasksEnabled()| is true.
+   */
+  virtual void PostNonNestableTask(std::unique_ptr<Task> task) {}
+
   /**
    * Schedules a task to be invoked by this TaskRunner. The task is scheduled
    * after the given number of seconds |delay_in_seconds|. The TaskRunner
@@ -64,7 +73,7 @@ class TaskRunner {
   /**
    * Schedules an idle task to be invoked by this TaskRunner. The task is
    * scheduled when the embedder is idle. Requires that
-   * TaskRunner::SupportsIdleTasks(isolate) is true. Idle tasks may be reordered
+   * |TaskRunner::IdleTasksEnabled()| is true. Idle tasks may be reordered
    * relative to other task types and may be starved for an arbitrarily long
    * time if no idle time is available. The TaskRunner implementation takes
    * ownership of |task|.
@@ -76,6 +85,11 @@ class TaskRunner {
    */
   virtual bool IdleTasksEnabled() = 0;
 
+  /**
+   * Returns true if non-nestable tasks are enabled for this TaskRunner.
+   */
+  virtual bool NonNestableTasksEnabled() const { return false; }
+
   TaskRunner() = default;
   virtual ~TaskRunner() = default;