Move Tab stats preferences to incognito whitelist.

Tab stats metrics preferences are moved to the persistent storage list
for incognito mode.
This CL does not make any behavioral change.

Bug: 861722
Change-Id: I052c8a62d4818a31451ff19baf815848bd3e3294
Reviewed-on: https://chromium-review.googlesource.com/1179145
Commit-Queue: Ramin Halavati <rhalavati@chromium.org>
Reviewed-by: Sébastien Marchand <sebmarchand@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584370}

chrome/browser/prefs/pref_service_incognito_whitelist.cc

@@ -125,6 +125,10 @@ const char* const kPersistentPrefNames[] = {
     // Google URL prefs don't store user data and just keep track of the URL.
     prefs::kLastKnownGoogleURL, prefs::kLastPromptedGoogleURL,
 
+    // Tab stats metrics are aggregated between regular and incognio mode.
+    prefs::kTabStatsTotalTabCountMax, prefs::kTabStatsMaxTabsPerWindow,
+    prefs::kTabStatsWindowCountMax, prefs::kTabStatsDailySample,
+
     // Rappor preferences are not used in incognito mode, but they are written
     // in startup if they don't exist. So if the startup would be in incognito,
     // they need to be persisted.
@@ -641,10 +645,6 @@ const char* const kTemporaryIncognitoWhitelist[] = {
 
     prefs::kMediaEngagementSchemaVersion,
 
-    // Preferences for recording metrics about tab and window usage.
-    prefs::kTabStatsTotalTabCountMax, prefs::kTabStatsMaxTabsPerWindow,
-    prefs::kTabStatsWindowCountMax, prefs::kTabStatsDailySample,
-
     prefs::kUnsafelyTreatInsecureOriginAsSecure,
 
     prefs::kIsolateOrigins, prefs::kSitePerProcess,