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

chrome/common/chrome_switches.cc

Index: chrome/common/chrome_switches.cc
===================================================================
--- chrome/common/chrome_switches.cc	(revision 163292)
+++ chrome/common/chrome_switches.cc	(working copy)
@@ -1540,6 +1540,12 @@
 // Windows 8 and higher.  Used when relaunching metro Chrome.
 const char kForceDesktop[]                   = "force-desktop";
 
+// Allows for disabling the overlapped I/O for TCP reads.
+// Possible values are "on" or "off".
+// The default is "on" which matches the existing behavior.

[rvargas (doing something else), 2012/10/23 00:19:40]

I'm a little confused by this. The "normal" pattern for field trials is to add a
command line to disable the trial, but the effect of this command line is to
force the client into the new behavior (basically get into the trial). What is
the use case?

[pmeenan, 2012/10/23 14:29:54]

The command line can force the trial on or off (force it explicitly to run in
one of the modes).  This is needed to allow for explicit testing in the lab of
overlapped reads vs event select reads.  If the field trial was 100% then I
could get by with a disable flag but since it is 50% this is the only way to
deterministically select a specific behavior.

I can switch it to a disable flag and do testing on dev builds but it would be a
lot easier if I could also do lab testing on production builds with flash and
everything else built in.

[rvargas (doing something else), 2012/10/24 18:48:09]

Thanks for the explanation... I figured it was for testing, but I missed that it
can disable the experiment as well. That works fine.

+// "off" switches to use non-blocking reads and WSAEventSelect.
+const char kOverlappedRead[]                 = "overlapped-reads";
+
 // Relaunches metro Chrome on Windows 8 and higher using a given shortcut.
 const char kRelaunchShortcut[]               = "relaunch-shortcut";