Add feature flag to enable/disable Translate.

This allows the user to enable/disable the Translate popup, either in
chrome://flags, or by using the `--disable-features=TranslateUI`
command-line flag.

Bug: 770776
Change-Id: I66af0ce5de568bafb45e0e501cb4f481ac6d6fb3
Reviewed-on: https://chromium-review.googlesource.com/1105311
Commit-Queue: Nicolas Ouellet-Payeur <[email protected]>
Reviewed-by: Michael Martis <[email protected]>
Reviewed-by: anthonyvd <[email protected]>
Cr-Commit-Position: refs/heads/master@{#568860}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 74ad0f2..8146bee 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -1089,6 +1089,9 @@
 extern const char kTranslateRankerEnforcementName[];
 extern const char kTranslateRankerEnforcementDescription[];
 
+extern const char kTranslateUIName[];
+extern const char kTranslateUIDescription[];
+
 extern const char kTreatInsecureOriginAsSecureName[];
 extern const char kTreatInsecureOriginAsSecureDescription[];