[scheduler] Add options to TaskQueue::InsertFence

third_party/WebKit/public/platform/scheduler/base/task_queue.h

Index: third_party/WebKit/public/platform/scheduler/base/task_queue.h
diff --git a/third_party/WebKit/public/platform/scheduler/base/task_queue.h b/third_party/WebKit/public/platform/scheduler/base/task_queue.h
index 4f48b0024cec6e19689cc5c8f130d600a5ff713e..527a2c54ff2e0a3f117d0b923cd284defa7f1079 100644
--- a/third_party/WebKit/public/platform/scheduler/base/task_queue.h
+++ b/third_party/WebKit/public/platform/scheduler/base/task_queue.h
@@ -172,12 +172,20 @@ class BLINK_PLATFORM_EXPORT TaskQueue : public base::SingleThreadTaskRunner {
   // Returns the queue's current TimeDomain.  Can be called from any thread.
   virtual TimeDomain* GetTimeDomain() const = 0;
 
+  enum class InsertFencePosition {
+    NOW,

[alex clarke (OOO till 29th), 2016/11/25 16:20:49]

I'm thinking ahead in case we ever add a third value so I'd suggest changing the
comments like so:

NOW,  // Tasks posted on the queue up till this point, and no further may run.

BEGINNING_OF_TIME,  // No tasks posted on this queue may run.

// Inserts a barrier into the task queue which prevents tasks with an enqueue
order
// greater the fence from running until either the fence has been removed or a
// subsequent fence has unblocked some tasks within the queue.
// Note delayed tasks, get their enqueue order set once their delay has expired,
// and non-delayed tasks get their enqueue order set when posted.

[altimin, 2016/11/25 16:59:26]

Done.

+    BEGINNING_OF_TIME,
+  };
+
   // Inserts a barrier into the task queue which inhibits non-delayed tasks
-  // posted after this point, or delayed tasks which are not yet ready to run,
-  // from being executed until the fence is cleared.  If a fence already existed
-  // the one supersedes it and previously blocked tasks will now run up until
-  // the new fence is hit.
-  virtual void InsertFence() = 0;
+  // posted after given point, or delayed tasks which are not yet ready to run,
+  // from being executed until the fence is cleared. If the fence is installed
+  // at the beginning of time, it will block all tasks in this queue,
+  // effectively disabling it.
+  //
+  // If a fence already existed the one supersedes it and previously blocked
+  // tasks will now run up until the new fence is hit.
+  virtual void InsertFence(InsertFencePosition position) = 0;
 
   // Removes any previously added fence and unblocks execution of any tasks
   // blocked by it.