[mojo-edk] Expose notification source to MojoWatch callbacks

mojo/public/cpp/system/watcher.cc

Index: mojo/public/cpp/system/watcher.cc
diff --git a/mojo/public/cpp/system/watcher.cc b/mojo/public/cpp/system/watcher.cc
index 57235338fe98c5f58ef05d4c44957dfc95add000..64f2b28927c77b0827df2f44bade25d9b06b631b 100644
--- a/mojo/public/cpp/system/watcher.cc
+++ b/mojo/public/cpp/system/watcher.cc
@@ -56,6 +56,10 @@ Watcher::~Watcher() {
     Cancel();
 }
 
+void Watcher::SetAllowSyncDispatch(bool allowed) {
+  allow_sync_dispatch_ = allowed;
+}
+
 bool Watcher::IsWatching() const {
   DCHECK(thread_checker_.CalledOnValidThread());
   return handle_.is_valid();
@@ -128,9 +132,15 @@ void Watcher::CallOnHandleReady(uintptr_t context,
   // 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