Adding pref to store the user-selected proximity threshold.

chrome/common/pref_names.cc

Index: chrome/common/pref_names.cc
diff --git a/chrome/common/pref_names.cc b/chrome/common/pref_names.cc
index efd6292c55ca5649630402ec26f52d20ef0fceba..9899a44981c955bfe647f2a4eea0e1007eef04f9 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -1340,6 +1340,10 @@ const char kEasyUnlockPairing[] = "easy_unlock.pairing";
 // in order to use Easy Unlock.
 const char kEasyUnlockProximityRequired[] = "easy_unlock.proximity_required";
 
+// How close the remote and the local device should be in order to use Easy
+// Unlock.
+const char kEasyUnlockProximityThreshold[] = "easy_unlock.proximity_threshold";
+
 #if BUILDFLAG(ENABLE_EXTENSIONS)
 // Used to indicate whether or not the toolbar redesign bubble has been shown
 // and acknowledged, and the last time the bubble was shown.