Add a new LaunchMode value for launches from a user experiment.

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 bd10931ff8f54268692cc63038f04fa476970a46..9f257f07fbadf9c9ce244a30c3c272abc30f4ec4 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -847,6 +847,10 @@ const char kUserAgent[]                     = "user-agent";
 // all of its state.
 const char kUserDataDir[]                   = "user-data-dir";
 
+// Experimental. Shows a dialog asking the user to try chrome. This flag is to
+// be used only by the upgrade process.
+const char kUserExperimentUx[] = "user-experiment-ux";

[Peter Kasting, 2017/05/26 00:57:41]

I'm not terribly keen on a switch called "user experiment UX" because that
sounds like it applies to practically every UX change we make.

Can we talk about toasts, or launching, or something more descriptive in this
name?  Based on the comment, "show-try-chrome-dialog"?  Or, based on the enum
description in the next file, "show-installer-retention-ui"? (And a similar
rename of the variable.)

Nit: Indent the initialization part even with the lines above and below

[grt (UTC plus 2), 2017/05/29 07:08:42]

We may as well re-use the existing --try-chrome-again switch. Thanks.

+
 // Uses experimental simple cache backend if possible.
 const char kUseSimpleCacheBackend[]         = "use-simple-cache-backend";