Implement local storage for App List in case app sync is off.

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 ecb95d072455e9e6a94c40461b86775107a6575e..9b223306ee19330af06df5de05d80d411b6b024c 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -2047,6 +2047,9 @@ const char kShelfAutoHideBehaviorLocal[] = "auto_hide_behavior_local";
 // index is also stored in the |kPinnedLauncherApp| pref. It may causes
 // creating two chrome icons.
 const char kShelfChromeIconIndex[] = "shelf_chrome_icon_index";
+// This value stores shelf positions to store pin position for local machine in
+// case sync app list is turned off.
+const char kShelfPins[] = "shelf_pins";
 // Dictionary value that holds per-display preference of shelf alignment and
 // auto-hide behavior. Key of the dictionary is the id of the display, and
 // its value is a dictionary whose keys are kShelfAlignment and