Let MojoSetDataPipeConsumerOptions() take null options.

mojo/public/c/system/tests/core_unittest.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.
 
 // This file tests the C API.
 
 #include <string.h>
 
 #include "mojo/public/c/system/buffer.h"
 #include "mojo/public/c/system/data_pipe.h"
@@ skipping 393 matching lines @@
 
   // Set the read threshold to 2.
   copts.struct_size = kCoptsSize;
   copts.read_threshold_num_bytes = 2u;
   EXPECT_EQ(MOJO_RESULT_OK, MojoSetDataPipeConsumerOptions(hc, &copts));
 
   // Should have the read threshold signal again.
   EXPECT_EQ(MOJO_RESULT_OK,
             MojoWait(hc, MOJO_HANDLE_SIGNAL_READ_THRESHOLD, 0, nullptr));
 
+  // Set the read threshold to the default by passing null, and check it.
+  EXPECT_EQ(MOJO_RESULT_OK, MojoSetDataPipeConsumerOptions(hc, nullptr));
+
+  memset(&copts, 255, kCoptsSize);
+  EXPECT_EQ(MOJO_RESULT_OK,
+            MojoGetDataPipeConsumerOptions(hc, &copts, kCoptsSize));
+  EXPECT_EQ(kCoptsSize, copts.struct_size);
+  EXPECT_EQ(0u, copts.read_threshold_num_bytes);
+
+  // Should still have the read threshold signal.
+  EXPECT_EQ(MOJO_RESULT_OK,
+            MojoWait(hc, MOJO_HANDLE_SIGNAL_READ_THRESHOLD, 0, nullptr));
+
   EXPECT_EQ(MOJO_RESULT_OK, MojoClose(hp));
   EXPECT_EQ(MOJO_RESULT_OK, MojoClose(hc));
 }
 
 // TODO(ncbray): enable this test once NaCl supports the corresponding APIs.
 #ifdef __native_client__
 #define MAYBE_BasicSharedBuffer DISABLED_BasicSharedBuffer
 #else
 #define MAYBE_BasicSharedBuffer BasicSharedBuffer
 #endif
@@ skipping 66 matching lines @@
 
 TEST(CoreTest, MinimalCppTest) {
   const char* failure = MinimalCppTest();
   EXPECT_FALSE(failure) << failure;
 }
 
 // TODO(vtl): Add multi-threaded tests.
 
 }  // namespace
 }  // namespace mojo