Add Desktop iOS promotion logging to chrome ios app.

ios/chrome/browser/pref_names.cc

Index: ios/chrome/browser/pref_names.cc
diff --git a/ios/chrome/browser/pref_names.cc b/ios/chrome/browser/pref_names.cc
index 0f75891881a2994a01b2fc19aac88864a4f13d39..5fccd808e994612005d6cbf21c10da80aff25f9e 100644
--- a/ios/chrome/browser/pref_names.cc
+++ b/ios/chrome/browser/pref_names.cc
@@ -139,4 +139,22 @@ const char kOmniboxGeolocationLastAuthorizationAlertVersion[] =
 const char kRateThisAppDialogLastShownTime[] =
     "ios.ratethisapp.dialog_last_shown_time";
 
+// Integer which indicates which desktop ios promotion initiated sending the SMS

[sdefresne, 2017/01/30 15:47:19]

ios -> iOS

What does "desktop ios" mean? I don't really understand this comment.
Would something like this work?

// Index of the entry point that initiated sending the SMS to the user for the
// "desktop to iOS" promotion (see corresponding histogram for details).

[mrefaat, 2017/01/30 16:32:23]

Acknowledged.

+// to the user.
+const char kDesktopIOSPromotionSMSEntryPoint[] =
+    "ios.desktop_ios_promo_sms_entrypoint";
+
+// Integer Which indicates which desktop ios promotions did the user see.

[sdefresne, 2017/01/30 15:47:19]

ditto

Maybe

// Indexes of the entry points presented to the user for "desktop to iOS"
promotion.

[mrefaat, 2017/01/30 16:32:23]

Acknowledged.

+const char kDesktopIOSPromotionShownEntryPoints[] =
+    "ios.desktop_ios_promo_shown_entrypoints";
+
+// Last desktop ios promotion impression (If SMS was sent it's the time of

[sdefresne, 2017/01/30 15:47:19]

ditto

Maybe

// Timestamp of the last "desktop to iOS" promotion SMS dispatch or of the last
// impression (if no SMS was sent).

[mrefaat, 2017/01/30 16:32:23]

Acknowledged.

+// sending the SMS).
+const char kDesktopIOSPromotionLastImpression[] =
+    "ios.desktop_ios_promo_last_impression";
+
+// True if the user see the promotion, get sms, install and sign into

[sdefresne, 2017/01/30 15:47:19]

ditto

Maybe

// True if the promotion was successful, i.e. user installed the application and
// signed in after being presented the promotion and receiving the SMS.

[mrefaat, 2017/01/30 16:32:23]

Acknowledged.

+// chrome ios.
+const char kDesktopIOSPromotionDone[] = "ios.desktop_ios_promo_done";
+
 }  // namespace prefs