Make MojoWaitMany() accept zero handles.

mojo/public/c/system/tests/wait_unittest.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.
 
 // This file tests the C wait API (the functions declared in
 // mojo/public/c/system/wait.h).
 
 #include "mojo/public/c/system/wait.h"
 
 #include "mojo/public/c/system/handle.h"
 #include "mojo/public/c/system/result.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace {
 
 TEST(WaitTest, InvalidHandle) {
   EXPECT_EQ(MOJO_RESULT_INVALID_ARGUMENT,
             MojoWait(MOJO_HANDLE_INVALID, ~MOJO_HANDLE_SIGNAL_NONE, 1000000u,
                      nullptr));
 
   const MojoHandle h = MOJO_HANDLE_INVALID;
   MojoHandleSignals sig = ~MOJO_HANDLE_SIGNAL_NONE;
   EXPECT_EQ(
       MOJO_RESULT_INVALID_ARGUMENT,
       MojoWaitMany(&h, &sig, 1u, MOJO_DEADLINE_INDEFINITE, nullptr, nullptr));
 }
 
+TEST(WaitTest, WaitManyNoHandles) {
+  EXPECT_EQ(MOJO_RESULT_DEADLINE_EXCEEDED,
+            MojoWaitMany(nullptr, nullptr, 0u, static_cast<MojoDeadline>(0),
+                         nullptr, nullptr));
+
+  // The |result_index| argument is optional, so make sure it doesn't touch it
+  // even if it's non-null.
+  // TODO(vtl): The same is true for the |signals_states| argument.
+  uint32_t result_index = static_cast<uint32_t>(-1);
+  EXPECT_EQ(MOJO_RESULT_DEADLINE_EXCEEDED,
+            MojoWaitMany(nullptr, nullptr, 0u, static_cast<MojoDeadline>(1000),
+                         &result_index, nullptr));
+  EXPECT_EQ(static_cast<uint32_t>(-1), result_index);
+}
+
 // TODO(vtl): Write tests that actually test waiting.
 
 }  // namespace