Refactor file path truncation into behavior

Change-Id: I21af00d3efc28291aa6918fde643cc6c77a7d05c
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.js b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.js
index fbd845a..ee12e34 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.js
+++ b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.js
@@ -14,9 +14,6 @@
 (function() {
   'use strict';
 
-  const COMMIT_MESSAGE_PATH = '/COMMIT_MSG';
-  const MERGE_LIST_PATH = '/MERGE_LIST';
-
   const ERR_REVIEW_STATUS = 'Couldn’t change file review status.';
   const MSG_LOADING_BLAME = 'Loading blame...';
   const MSG_LOADED_BLAME = 'Blame loaded';
@@ -142,6 +139,7 @@
     behaviors: [
       Gerrit.KeyboardShortcutBehavior,
       Gerrit.PatchSetBehavior,
+      Gerrit.PathListBehavior,
       Gerrit.RESTClientBehavior,
     ],
 
@@ -495,7 +493,7 @@
       // has been queued, the event can bubble up to the handler in gr-app.
       this.async(() => {
         this.fire('title-change',
-            {title: this._computeTruncatedFileDisplayName(this._path)});
+            {title: this.computeTruncatedPath(this._path)});
       });
 
       // When navigating away from the page, there is a possibility that the
@@ -568,7 +566,7 @@
     _pathChanged(path) {
       if (path) {
         this.fire('title-change',
-            {title: this._computeTruncatedFileDisplayName(path)});
+            {title: this.computeTruncatedPath(path)});
       }
 
       if (this._fileList.length == 0) { return; }
@@ -640,19 +638,6 @@
       return this._getChangePath(change, patchRangeRecord.base, revisions);
     },
 
-    _computeFileDisplayName(path) {
-      if (path === COMMIT_MESSAGE_PATH) {
-        return 'Commit message';
-      } else if (path === MERGE_LIST_PATH) {
-        return 'Merge list';
-      }
-      return path;
-    },
-
-    _computeTruncatedFileDisplayName(path) {
-      return util.truncatePath(this._computeFileDisplayName(path));
-    },
-
     _computeFileSelected(path, currentPath) {
       return path == currentPath;
     },