Adds a flag to support "Virtual Time" to the blink scheduler

components/scheduler/base/nestable_single_thread_task_runner.h

Index: components/scheduler/base/nestable_single_thread_task_runner.h
diff --git a/components/scheduler/base/nestable_single_thread_task_runner.h b/components/scheduler/base/nestable_single_thread_task_runner.h
index 2fc7c28f2837181cd729a22dffb7ff901c108c43..ad27fa7c3ab9d9820981f5663bd18eedc67c6e46 100644
--- a/components/scheduler/base/nestable_single_thread_task_runner.h
+++ b/components/scheduler/base/nestable_single_thread_task_runner.h
@@ -5,15 +5,17 @@
 #ifndef COMPONENTS_SCHEDULER_BASE_NESTABLE_SINGLE_THREAD_TASK_RUNNER_H_
 #define COMPONENTS_SCHEDULER_BASE_NESTABLE_SINGLE_THREAD_TASK_RUNNER_H_
 
-#include "base/single_thread_task_runner.h"
 #include "base/message_loop/message_loop.h"
+#include "base/single_thread_task_runner.h"
+#include "base/time/tick_clock.h"
 #include "components/scheduler/scheduler_export.h"
 
 namespace scheduler {
 
 // A single thread task runner which exposes whether it is running nested.
 class SCHEDULER_EXPORT NestableSingleThreadTaskRunner

[Sami, 2015/10/28 20:00:34]

I think this interface needs a better name now that it also deals with time.
Subclasses probably too.

TaskQueueManagerDelegate is straightforward but wordy.

[alex clarke (OOO till 29th), 2015/10/29 18:07:30]

Done.

-    : public base::SingleThreadTaskRunner {
+    : public base::SingleThreadTaskRunner,
+      public base::TickClock {
  public:
   NestableSingleThreadTaskRunner() {}
 
@@ -21,6 +23,10 @@ class SCHEDULER_EXPORT NestableSingleThreadTaskRunner
   // a nested task).
   virtual bool IsNested() const = 0;
 
+  // Used by the TaskQueueManager to tell us there is no more non-delayed work
+  // to do.
+  virtual void OnNoMoreWork() = 0;

[Sami, 2015/10/28 20:00:34]

I think it's a little weird that this method is here rather than on the
observer, especially since only one NestableSingleThreadTaskRunner cares about
this notification.

Didn't we recently talk about adding a similar idle observer for another patch?
WDYT of doing that here?

[alex clarke (OOO till 29th), 2015/10/29 18:07:30]

Turns out to be really hard to get the interface right.  As discussed offline
lets revisit this later.

+
  protected:
   ~NestableSingleThreadTaskRunner() override {}