Add a perf test for async wait and fix a bug in mojo::RunLoop.

mojo/public/cpp/utility/lib/run_loop.cc

 // Copyright 2014 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/utility/run_loop.h"
 
 #include <assert.h>
 #include <pthread.h>
 
 #include <algorithm>
@@ skipping 327 matching lines @@
   for (const auto& result : results) {
     auto id = result.cookie;
     auto it = handlers_.find(id);
     // Though we should find an entry for the first result, a handler that we
     // invoke may remove other handlers.
     if (it == handlers_.end())
       continue;
 
     auto handler = it->second.handler;
     handlers_.erase(it);
+    MojoResult r = WaitSetRemove(wait_set_.get(), id);
+    MOJO_ALLOW_UNUSED_LOCAL(r);
+    assert(r == MOJO_RESULT_OK);
     if (result.wait_result == MOJO_RESULT_OK)
       handler->OnHandleReady(id);
     else
       handler->OnHandleError(id, result.wait_result);
     did_work = true;
 
     if (current_run_state_->should_quit)
       break;
   }
   return did_work;
@@ skipping 26 matching lines @@
     handler->OnHandleError(id, MOJO_RESULT_DEADLINE_EXCEEDED);
     did_work = true;
 
     if (current_run_state_->should_quit)
       break;
   }
   return did_work;
 }
 
 }  // namespace mojo