Use a dedicated command line flag for FIFO IPC channels on POSIX.

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 a33043a25da43037cf3e3701023302d06639209a..c4b4512b0be25f8c738b4234f3f4174e4831345a 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -388,4 +388,8 @@ const wchar_t kTestName[]                      = L"test-name";
 // command line. (Useful values might be "valgrind" or "gdb --args")
 const wchar_t kRendererCmdPrefix[]             = L"renderer-cmd-prefix";
 
+// On POSIX only: use FIFO for IPC channels so that "unrelated" process
+// can connect to a channel, provided it knows its name. For debugging purposes.
+const wchar_t kIPCUseFIFO[]                    = L"ipc-use-fifo";
+
 }  // namespace switches