signin: force web signin flow initiated visits to accounts.google.com to their own process.

chrome/common/chrome_switches.cc

Index: chrome/common/chrome_switches.cc
diff --git a/chrome/common/chrome_switches.cc b/chrome/common/chrome_switches.cc
index 61875f80f74f6cda19942b7aad4d401f2e3bb8cf..109423efe6d3bd1cc0cb79304a2db45dccd1e755 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -1228,6 +1228,9 @@ const char kShowIcons[]                     = "show-icons";
 // If true the alignment of the launcher can be changed.
 const char kShowLauncherAlignmentMenu[]     = "show-launcher-alignment-menu";
 
+// Marks a renderer as the signin process.
+const char kSigninProcess[]                 = "signin-process";
+
 // Enables or disables sideload wipeout extension effort.
 const char kSideloadWipeout[]               = "sideload-wipeout";