[SPDY] Do not advertise SPDY/2 by default

chrome/browser/io_thread.h

Index: chrome/browser/io_thread.h
diff --git a/chrome/browser/io_thread.h b/chrome/browser/io_thread.h
index 9901afdacb8cd2eda4700dcbab905abedfbdf6e6..e5187f4185a5362f1ff6767e06fbe024b4e35d65 100644
--- a/chrome/browser/io_thread.h
+++ b/chrome/browser/io_thread.h
@@ -221,8 +221,8 @@ class IOThread : public content::BrowserThreadDelegate {
 
   void InitializeNetworkOptions(const CommandLine& parsed_command_line);
 
-  // Enable the SPDY protocol.  If this function is not called, SPDY/3
-  // will be enabled.
+  // Enable SPDY with the given mode, which may contain the following:

[darin (slow to review), 2013/10/05 06:27:58]

side-note: io_thread.h seems like the wrong place to be describing the format of
a mode string. it seems like this functionality could be broken out into a
separate file that lives in browser/net/ or elsewhere more net specific.

that might be good cleanup for most of the net related things in this class.

[akalin, 2013/10/05 19:40:17]

Yeah, that's crbug.com/190061 . i'll get to it one of these days...

+  //
   //   "off"                      : Disables SPDY support entirely.
   //   "ssl"                      : Forces SPDY for all HTTPS requests.
   //   "no-ssl"                   : Forces SPDY for all HTTP requests.
@@ -230,7 +230,7 @@ class IOThread : public content::BrowserThreadDelegate {
   //   "exclude=<host>"           : Disables SPDY support for the host <host>.
   //   "no-compress"              : Disables SPDY header compression.
   //   "no-alt-protocols          : Disables alternate protocol support.
-  //   "force-alt-protocols       : Forces an alternate protocol of SPDY/2
+  //   "force-alt-protocols       : Forces an alternate protocol of SPDY/3
   //                                on port 443.
   //   "single-domain"            : Forces all spdy traffic to a single domain.
   //   "init-max-streams=<limit>" : Specifies the maximum number of concurrent