Do not write the Bookmarks Activity view mode preference unnecessarily.

Fix for issue 2891872

Change-Id: Ia42b70bebe99d88562bba0de87913beec16d648c
diff --git a/src/com/android/browser/BrowserBookmarksPage.java b/src/com/android/browser/BrowserBookmarksPage.java
index cd2abd9..4d5c5fa 100644
--- a/src/com/android/browser/BrowserBookmarksPage.java
+++ b/src/com/android/browser/BrowserBookmarksPage.java
@@ -293,11 +293,13 @@
         mViewMode = viewMode;
 
         // Update the preferences to make the new view mode sticky.
-        Editor ed = getPreferences(MODE_PRIVATE).edit();
-        if (mMostVisited) {
-            ed.putInt(PREF_MOST_VISITED_VIEW_MODE, mViewMode.ordinal());
-        } else {
-            ed.putInt(PREF_BOOKMARK_VIEW_MODE, mViewMode.ordinal());
+        SharedPreferences preferences = getPreferences(MODE_PRIVATE);
+        Editor ed = preferences.edit();
+        int pref = mViewMode.ordinal();
+        if (mMostVisited && preferences.getInt(PREF_MOST_VISITED_VIEW_MODE, -1) != pref) {
+            ed.putInt(PREF_MOST_VISITED_VIEW_MODE, pref);
+        } else if (!mMostVisited && preferences.getInt(PREF_BOOKMARK_VIEW_MODE, -1) != pref) {
+            ed.putInt(PREF_BOOKMARK_VIEW_MODE, pref);
         }
         ed.commit();