Add back pipelining after M17 branch point.

chrome/common/chrome_switches.cc

Index: chrome/common/chrome_switches.cc
===================================================================
--- chrome/common/chrome_switches.cc	(revision 113256)
+++ chrome/common/chrome_switches.cc	(working copy)
@@ -485,6 +485,11 @@
 // for example page cycler and layout tests. See bug 1157243.
 const char kEnableFileCookies[]             = "enable-file-cookies";
 
+// Enable HTTP pipelining. Attempt to pipeline HTTP connections. Heuristics will
+// try to figure out if pipelining can be used for a given host and request.
+// Without this flag, pipelining will never be used.
+const char kEnableHttpPipelining[]          = "enable-http-pipelining";
+
 // Enables the in-browser thumbnailing, which is more efficient than the
 // in-renderer thumbnailing, as we can use more information to determine if we
 // need to update thumbnails.