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 721b34d0b3705d727cf11710ae03ea78edb6e472..28015e158ec0e1a27f907584c829e4cedbbe0255 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -1220,6 +1220,9 @@ 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";