Fixed flakiness in WebGL conformance, and presumably other tests, under Telemetry.

chrome/common/benchmarking_messages.h

 // Copyright (c) 2011 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.
 
 // Multiply-included file, no traditional include guard.
 
 #include <string>
 
 #include "base/basictypes.h"
 #include "build/build_config.h"
 
 #include "ipc/ipc_message_macros.h"
 #include "ui/gfx/native_widget_types.h"
 
 #define IPC_MESSAGE_START ChromeBenchmarkingMsgStart
 
 // Message sent from the renderer to the browser to request that the browser
 // close all sockets.  Used for debugging/testing.
-IPC_MESSAGE_CONTROL0(ChromeViewHostMsg_CloseCurrentConnections)
+//
+// This message must be synchronous so that the test harness can not
+// issue further network requests before it completes.
+IPC_SYNC_MESSAGE_CONTROL0_0(ChromeViewHostMsg_CloseCurrentConnections)

[tonyg, 2013/09/04 00:02:24]

lgtm as long as you've verified that the comment stating this is only used for
debugging/testing is still accurate.

[Ken Russell (switch to Gerrit), 2013/09/04 17:18:59]

The comment's still accurate. This message is ignored unless the net
benchmarking extension's been enabled.

 
 // Message sent from the renderer to the browser to request that the browser
 // enable or disable the cache.  Used for debugging/testing.
 IPC_MESSAGE_CONTROL1(ChromeViewHostMsg_SetCacheMode,
                      bool /* enabled */)
 
 // Message sent from the renderer to the browser to request that the browser
 // clear the cache.  Used for debugging/testing.
 // |result| is the returned status from the operation.
 IPC_SYNC_MESSAGE_CONTROL0_1(ChromeViewHostMsg_ClearCache,
                             int /* result */)
 
 // Message sent from the renderer to the browser to request that the browser
 // clear the host cache.  Used for debugging/testing.
 // |result| is the returned status from the operation.
 IPC_SYNC_MESSAGE_CONTROL0_1(ChromeViewHostMsg_ClearHostResolverCache,
                             int /* result */)
 
 // Message sent from the renderer to the browser to request that the browser
 // enable or disable spdy.  Used for debugging/testing/benchmarking.
 IPC_MESSAGE_CONTROL1(ChromeViewHostMsg_EnableSpdy,
                      bool /* enable */)
 
 // Message sent from the renderer to the browser to request that the browser
 // clear the predictor cache.  Used for debugging/testing.
 // |result| is the returned status from the operation.
 IPC_SYNC_MESSAGE_CONTROL0_1(ChromeViewHostMsg_ClearPredictorCache,
                             int /* result */)