Switch the TCP reads on Windows to use non-blocking/non-async I/O.

chrome/browser/chrome_browser_field_trials.cc

Index: chrome/browser/chrome_browser_field_trials.cc
===================================================================
--- chrome/browser/chrome_browser_field_trials.cc	(revision 161340)
+++ chrome/browser/chrome_browser_field_trials.cc	(working copy)
@@ -28,6 +28,9 @@
 #include "net/http/http_stream_factory.h"
 #include "net/socket/client_socket_pool_base.h"
 #include "net/socket/client_socket_pool_manager.h"
+#if defined(OS_WIN)
+#include "net/socket/tcp_client_socket_win.h"
+#endif  // defined(OS_WIN)

[Ryan Sleevi, 2012/10/12 18:53:13]

style nit: Platform defines like go after the 'standard' headers (eg: move line
32 to between lines 38 and 39)

[pmeenan, 2012/10/17 15:12:31]

Done.

 #include "net/spdy/spdy_session.h"
 #include "net/spdy/spdy_session_pool.h"
 #include "ui/base/layout.h"
@@ -129,6 +132,7 @@
   SetUpSafeBrowsingInterstitialFieldTrial();
   SetUpInfiniteCacheFieldTrial();
   SetUpCacheSensitivityAnalysisFieldTrial();
+  WindowsOverlappedTCPReadsFieldTrial();
 #if defined(ENABLE_ONE_CLICK_SIGNIN)
   OneClickSigninHelper::InitializeFieldTrial();
 #endif
@@ -587,3 +591,29 @@
   trial->AppendGroup("400A", sensitivity_analysis_probability);
   trial->AppendGroup("400B", sensitivity_analysis_probability);
 }
+
+void ChromeBrowserFieldTrials::WindowsOverlappedTCPReadsFieldTrial() {

[Ryan Sleevi, 2012/10/12 18:53:13]

style: Please review this function for whitespace issues

[pmeenan, 2012/10/17 15:12:31]

Done.

+#if defined(OS_WIN)
+  if (parsed_command_line_.HasSwitch(switches::kOverlappedRead)) {
+    std::string option = parsed_command_line_.GetSwitchValueASCII(
+                                switches::kOverlappedRead);
+    if (LowerCaseEqualsASCII(option, "off")) {
+      net::TCPClientSocketWin::DisableOverlappedReads();
+    }

[Ryan Sleevi, 2012/10/12 18:53:13]

style nit: the bracing style in this file is to omit { } for one-line
conditionals (see also line 613-615)

[pmeenan, 2012/10/17 15:12:31]

Done.

+  } else {
+    const base::FieldTrial::Probability kDivisor = 2;  // 1 in 2 chance
+    const base::FieldTrial::Probability kOverlappedReadProbability = 1;
+    scoped_refptr<base::FieldTrial> nbread_trial(
+        base::FieldTrialList::FactoryGetFieldTrial("OverlappedReadImpact",
+                         kDivisor, "OverlappedReadEnabled", 2015, 1, 1, NULL));

[Ryan Sleevi, 2012/10/12 18:53:13]

That's a really long trial. Are you sure that's the desired time frame?

When do you expect to make a decision about whether this is correct? 3 months
from now? 6 months? Try to scope the trial to the point where you need to make a
decision.

[pmeenan, 2012/10/17 15:12:31]

Done.

+    int overlapped_reads_disabled_group =
+        nbread_trial->AppendGroup("OverlappedReadDisabled",
+                                  kOverlappedReadProbability);
+    int assigned_group = nbread_trial->group();
+    if (assigned_group == overlapped_reads_disabled_group) {
+      net::TCPClientSocketWin::DisableOverlappedReads();
+    }
+  }
+#endif
+}
+