Experimentally strictify third-party cookie blocking.

chrome/browser/chrome_browser_main.cc

 // 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.
 
 #include "chrome/browser/chrome_browser_main.h"
 
 #include <algorithm>
 #include <string>
 #include <vector>
 
@@ skipping 1341 matching lines @@
   // call to ConvertFlagsToSwitches in the following line.
   if (!parsed_command_line().HasSwitch(switches::kViewsDesktop))
     CommandLine::ForCurrentProcess()->AppendSwitchASCII(switches::kViewsDesktop,
                                                         "other");
 #elif defined(USE_AURA) && defined(OS_LINUX)
   // Always add the --views-desktop flag, if not already set.
   if (!parsed_command_line().HasSwitch(switches::kViewsDesktop))
     CommandLine::ForCurrentProcess()->AppendSwitch(switches::kViewsDesktop);
 #endif
 
+  // Always add the --block-reading-third-party-cookies flag, if not already
+  // set. We'll leave this on for a bit to determine if we Break The Web for
+  // Canary users.
+  //
+  // TODO(mkwst): Remove this once impact is clear (http://crbug.com/98241).
+  if (!parsed_command_line().HasSwitch(
+      switches::kBlockReadingThirdPartyCookies))
+    CommandLine::ForCurrentProcess()->AppendSwitch(
+        switches::kBlockReadingThirdPartyCookies);
+
   // Convert active labs into switches. Modifies the current command line.
   about_flags::ConvertFlagsToSwitches(local_state,
                                       CommandLine::ForCurrentProcess());
 
   // Reset the command line in the crash report details, since we may have
   // just changed it to include experiments.
   child_process_logging::SetCommandLine(CommandLine::ForCurrentProcess());
 
 #if defined(TOOLKIT_VIEWS)
   views::Widget::SetPureViews(
@@ skipping 692 matching lines @@
   if (env->GetVar(chrome::kPreReadEnvironmentVariable, &pre_read) &&
       (pre_read == "0" || pre_read == "1")) {
     std::string uma_name(name);
     uma_name += "_PreRead";
     uma_name += pre_read == "1" ? "Enabled" : "Disabled";
     AddPreReadHistogramTime(uma_name.c_str(), time);
   }
 #endif
 #endif
 }