Add an about://flag for freezing the User-Agent header

Bug: 955620
Change-Id: I453e9d11f53ae47387a358d33199c3ccae07a243
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2014122
Commit-Queue: Aaron Tagliaboschi <[email protected]>
Reviewed-by: Elly Fong-Jones <[email protected]>
Reviewed-by: Avi Drissman <[email protected]>
Cr-Commit-Position: refs/heads/master@{#734919}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 98727789..1b6b576 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -639,6 +639,9 @@
 extern const char kFractionalScrollOffsetsName[];
 extern const char kFractionalScrollOffsetsDescription[];
 
+extern const char kFreezeUserAgentName[];
+extern const char kFreezeUserAgentDescription[];
+
 extern const char kForceEffectiveConnectionTypeName[];
 extern const char kForceEffectiveConnectionTypeDescription[];
 extern const char kEffectiveConnectionTypeUnknownDescription[];