Migrate TabPersistentStore to one shared directory for multi-instance

chrome/android/java/src/org/chromium/chrome/browser/compositor/layouts/content/TabContentManager.java

Index: chrome/android/java/src/org/chromium/chrome/browser/compositor/layouts/content/TabContentManager.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/compositor/layouts/content/TabContentManager.java b/chrome/android/java/src/org/chromium/chrome/browser/compositor/layouts/content/TabContentManager.java
index a4072a5c863abb831dc45fd02c82397f7796c6d3..908eab71cfb812f98423695686ece83ceef1f835 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/compositor/layouts/content/TabContentManager.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/compositor/layouts/content/TabContentManager.java
@@ -321,10 +321,8 @@ public class TabContentManager {
 
         // BUG: We support multiple tab model selectors, and they all share the same thumbnail
         // directory. This cleanup code checks only the current model selector to see if the
-        // thumbnails are no longer used. It should instead:
-        // a) consult with *all* tab model selectors (which may not even be in memory)
-        // b) use separate thumbnail directories for each tab model (perhaps using hardlink to
-        //    eliminate disk overhead)
+        // thumbnails are no longer used. It should instead consult with *all* tab model selectors
+        // (which may not even be in memory).
         new AsyncTask<Void, Void, String[]>() {
             @Override
             protected String[] doInBackground(Void... voids) {