[mojo-bindings] Use Watcher API for JS bindings

mojo/edk/js/waiting_callback.cc

Index: mojo/edk/js/waiting_callback.cc
diff --git a/mojo/edk/js/waiting_callback.cc b/mojo/edk/js/waiting_callback.cc
index af34d87ef801c3fcd1a5d2331595b040de975b70..ef702c8a28bfbdcea86a54e03dee34e7fd26ed9d 100644
--- a/mojo/edk/js/waiting_callback.cc
+++ b/mojo/edk/js/waiting_callback.cc
@@ -28,31 +28,57 @@ gin::Handle<WaitingCallback> WaitingCallback::Create(
     v8::Isolate* isolate,
     v8::Handle<v8::Function> callback,
     gin::Handle<HandleWrapper> handle_wrapper,
-    MojoHandleSignals signals) {
+    MojoHandleSignals signals,
+    bool one_shot) {
   gin::Handle<WaitingCallback> waiting_callback = gin::CreateHandle(
-      isolate, new WaitingCallback(isolate, callback, handle_wrapper));
-
-  waiting_callback->handle_watcher_.Start(
-      handle_wrapper->get(), signals, MOJO_DEADLINE_INDEFINITE,
-      base::Bind(&WaitingCallback::OnHandleReady,
-                 base::Unretained(waiting_callback.get())));
+      isolate,
+      new WaitingCallback(isolate, callback, handle_wrapper, one_shot));
+
+  if (one_shot) {
+    waiting_callback->handle_watcher_.Start(
+        handle_wrapper->get(), signals, MOJO_DEADLINE_INDEFINITE,
+        base::Bind(&WaitingCallback::OnHandleReady,
+                   base::Unretained(waiting_callback.get())));
+  } else {
+    waiting_callback->watcher_.Start(
+        handle_wrapper->get(), signals,
+        base::Bind(&WaitingCallback::OnHandleReady,
+                   base::Unretained(waiting_callback.get())));
+  }
   return waiting_callback;
 }
 
 void WaitingCallback::Cancel() {
-  if (!handle_watcher_.is_watching())
+  if (!handle_watcher_.is_watching() && !watcher_.IsWatching())
     return;
 
-  RemoveHandleCloseObserver();
-  handle_watcher_.Stop();
+  if (handle_watcher_.is_watching()) {
+    DCHECK(one_shot_);
+    DCHECK(!watcher_.IsWatching());
+    RemoveHandleCloseObserver();
+    handle_watcher_.Stop();
+  } else {
+    DCHECK(!one_shot_);
+    DCHECK(watcher_.IsWatching());
+    watcher_.Cancel();
+    handle_wrapper_ = nullptr;
+  }
 }
 
 WaitingCallback::WaitingCallback(v8::Isolate* isolate,
                                  v8::Handle<v8::Function> callback,
-                                 gin::Handle<HandleWrapper> handle_wrapper)
-    : handle_wrapper_(handle_wrapper.get()),
+                                 gin::Handle<HandleWrapper> handle_wrapper,
+                                 bool one_shot)
+    : one_shot_(one_shot),
+      handle_wrapper_(handle_wrapper.get()),
       weak_factory_(this) {
-  handle_wrapper_->AddCloseObserver(this);
+  if (one_shot_) {
+    // We need to manually signal cancellation if the handle is closed while
+    // waiting in one-shot mode. When using non-one-shot mode this cancellation
+    // behavior is already provided for us.
+    handle_wrapper_->AddCloseObserver(this);
+  }
+
   v8::Handle<v8::Context> context = isolate->GetCurrentContext();
   runner_ = gin::PerContextData::From(context)->runner()->GetWeakPtr();
   GetWrapper(isolate)
@@ -65,18 +91,27 @@ WaitingCallback::~WaitingCallback() {
 }
 
 void WaitingCallback::RemoveHandleCloseObserver() {
+  DCHECK(one_shot_);
   handle_wrapper_->RemoveCloseObserver(this);
   handle_wrapper_ = nullptr;
 }
 
 void WaitingCallback::OnHandleReady(MojoResult result) {
-  RemoveHandleCloseObserver();
+  if (one_shot_)
+    RemoveHandleCloseObserver();
+
   CallCallback(result);
 }
 
 void WaitingCallback::CallCallback(MojoResult result) {
-  DCHECK(!handle_watcher_.is_watching());
-  DCHECK(!handle_wrapper_);
+  DCHECK(
+    // Either this is a one-shot callback and its HandleWatcher should have been
+    // stopped already...
+    (one_shot_ && !handle_wrapper_ && !handle_watcher_.is_watching()) ||
+    // Or it's not a one-shot callback and the Watcher is either still active or
+    // was implicitly cancelled and this is a notification of that fact.
+    (!one_shot_ && handle_wrapper_ &&
+        (watcher_.IsWatching() || result == MOJO_RESULT_CANCELLED)));
 
   if (!runner_)
     return;
@@ -97,6 +132,8 @@ void WaitingCallback::CallCallback(MojoResult result) {
 }
 
 void WaitingCallback::OnWillCloseHandle() {
+  DCHECK(one_shot_);
+
   handle_watcher_.Stop();
 
   // This may be called from GC, so we can't execute Javascript now, call
@@ -105,7 +142,7 @@ void WaitingCallback::OnWillCloseHandle() {
   base::MessageLoop::current()->PostTask(
       FROM_HERE,
       base::Bind(&WaitingCallback::CallCallback, weak_factory_.GetWeakPtr(),
-                 MOJO_RESULT_INVALID_ARGUMENT));
+                 MOJO_RESULT_CANCELLED));
 }
 
 }  // namespace js