Add more tests for AwakableList (esp. persistent vs one-shot awakables).

mojo/edk/system/awakable_list.cc

 // Copyright 2013 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/edk/system/awakable_list.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 #include "mojo/edk/system/awakable.h"
@@ skipping 19 matching lines @@
       // Persistent awakables are called for all changes on watched signals.
       if ((new_state.satisfied_signals & it->signals) !=
               (old_state.satisfied_signals & it->signals) ||
           (new_state.satisfiable_signals & it->signals) !=
               (old_state.satisfiable_signals & it->signals)) {
         awoken = true;
         it->awakable->Awake(it->context, Awakable::AwakeReason::CHANGED,
                             new_state);
       }
     } else {
-      // One-shot awakables are only called on "leading edge" changes.
+      // One-shot awakables are only called on "leading edge" changes in overall
+      // satisfied-ness or never-satisfiable-ness. (That is, if a one-shot
+      // awakable was previously satisfied and is still satisfied, but for
+      // different reasons, it will not be called.)
       if (new_state.satisfies(it->signals) &&
           !old_state.satisfies(it->signals)) {
         awoken = true;
         it->awakable->Awake(it->context, Awakable::AwakeReason::SATISFIED,
                             new_state);
       } else if (!new_state.can_satisfy(it->signals) &&
                  old_state.can_satisfy(it->signals)) {
         awoken = true;
         it->awakable->Awake(it->context, Awakable::AwakeReason::UNSATISFIABLE,
                             new_state);
@@ skipping 39 matching lines @@
       std::swap(*it, *last);
     } else {
       ++it;
     }
   }
   awakables_.erase(last, awakables_.end());
 }
 
 }  // namespace system
 }  // namespace mojo