Expose RunsTasksOnCurrentThread through WebTaskRunner

third_party/WebKit/public/platform/WebTaskRunner.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef WebTaskRunner_h
 #define WebTaskRunner_h
 
 #include "WebCommon.h"
 
 #ifdef INSIDE_BLINK
@@ skipping 21 matching lines @@
     // Takes ownership of |Task|. Can be called from any thread.
     virtual void postTask(const WebTraceLocation&, Task*) = 0;
 
     // Schedule a task to be run after |delayMs| on the the associated WebThread.
     // Takes ownership of |Task|. Can be called from any thread.
     virtual void postDelayedTask(const WebTraceLocation&, Task*, double delayMs) = 0;
 
     // Returns a clone of the WebTaskRunner.
     virtual WebTaskRunner* clone() = 0;
 
+    // Returns true if a posted task runs on the current thread.
+    // Can be called from any thread.

[kinuko, 2016/07/05 14:09:19]

This description sounds like a runner is always tied to a thread, while I think
we're in general trying to avoid introducing such assumptions over task runners.
  base's same method has more subtle description, which is still confusing but
trying to avoid introducing strong tie to a thread... probably we should follow
that (or give it a better name).

[tzik, 2016/07/05 15:22:40]

Borrowed it from base...

+    virtual bool runsTasksOnCurrentThread() = 0;
+
     // ---
 
     // Headless Chrome virtualises time for determinism and performance (fast forwarding
     // of timers). To make this work some parts of blink (e.g. Timers) need to use virtual
     // time, however by default new code should use the normal non-virtual time APIs.
 
     // Returns a double which is the number of seconds since epoch (Jan 1, 1970).
     // This may represent either the real time, or a virtual time depending on
     // whether or not the WebTaskRunner is associated with a virtual time domain or a
     // real time domain.
@@ skipping 19 matching lines @@
     std::unique_ptr<WebTaskRunner> adoptClone()
     {
         return wrapUnique(clone());
     }
 #endif
 };
 
 } // namespace blink
 
 #endif // WebTaskRunner_h