[mojo-edk] Expose notification source to MojoWatch callbacks

mojo/public/cpp/system/watcher.cc

 // Copyright 2016 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.
 
 #include "mojo/public/cpp/system/watcher.h"
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/macros.h"
 #include "base/message_loop/message_loop.h"
@@ skipping 38 matching lines @@
     : task_runner_(base::ThreadTaskRunnerHandle::Get()),
       weak_factory_(this) {
   weak_self_ = weak_factory_.GetWeakPtr();
 }
 
 Watcher::~Watcher() {
   if(IsWatching())
     Cancel();
 }
 
+void Watcher::SetAllowSyncDispatch(bool allowed) {
+  allow_sync_dispatch_ = allowed;
+}
+
 bool Watcher::IsWatching() const {
   DCHECK(thread_checker_.CalledOnValidThread());
   return handle_.is_valid();
 }
 
 MojoResult Watcher::Start(Handle handle,
                           MojoHandleSignals signals,
                           const ReadyCallback& callback) {
   DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK(!IsWatching());
@@ skipping 52 matching lines @@
 // static
 void Watcher::CallOnHandleReady(uintptr_t context,
                                 MojoResult result,
                                 MojoHandleSignalsState signals_state) {
   // NOTE: It is safe to assume the Watcher still exists because this callback
   // will never be run after the Watcher's destructor.
   //
   // TODO: Maybe we should also expose |signals_state| throught he Watcher API.
   // Current HandleWatcher users have no need for it, so it's omitted here.
   Watcher* watcher = reinterpret_cast<Watcher*>(context);
-  watcher->task_runner_->PostTask(
-      FROM_HERE,
-      base::Bind(&Watcher::OnHandleReady, watcher->weak_self_, result));
+
+  if (watcher->task_runner_->RunsTasksOnCurrentThread() &&
+      watcher->allow_sync_dispatch_) {
+    watcher->OnHandleReady(result);
+  } else {
+    watcher->task_runner_->PostTask(
+        FROM_HERE,
+        base::Bind(&Watcher::OnHandleReady, watcher->weak_self_, result));
+  }
 }
 
 }  // namespace mojo