Revise the shelf alignment locking mechanism.

chrome/browser/ui/ash/chrome_launcher_prefs.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/ash/chrome_launcher_prefs.h"
 
 #include <stddef.h>
 
 #include <memory>
 
@@ skipping 114 matching lines @@
 }
 
 const char* AlignmentToPref(ShelfAlignment alignment) {
   switch (alignment) {
     case SHELF_ALIGNMENT_BOTTOM:
       return kShelfAlignmentBottom;
     case SHELF_ALIGNMENT_LEFT:
       return kShelfAlignmentLeft;
     case SHELF_ALIGNMENT_RIGHT:
       return kShelfAlignmentRight;
+    case SHELF_ALIGNMENT_LOCKED:
+      // This should not be a valid preference option for now. We only want to
+      // lock the shelf during login or when adding a user.
+      return nullptr;
   }
   NOTREACHED();
   return nullptr;
 }
 
 ShelfAutoHideBehavior AutoHideBehaviorFromPref(const std::string& value) {
   // Note: To maintain sync compatibility with old images of chrome/chromeos
   // the set of values that may be encountered includes the now-extinct
   // "Default" as well as "Never" and "Always", "Default" should now
   // be treated as "Never" (http://crbug.com/146773).
   if (value == kShelfAutoHideBehaviorAlways)
     return SHELF_AUTO_HIDE_BEHAVIOR_ALWAYS;
   return SHELF_AUTO_HIDE_BEHAVIOR_NEVER;
 }
 
 const char* AutoHideBehaviorToPref(ShelfAutoHideBehavior behavior) {
   switch (behavior) {
     case SHELF_AUTO_HIDE_BEHAVIOR_ALWAYS:
       return kShelfAutoHideBehaviorAlways;
     case SHELF_AUTO_HIDE_BEHAVIOR_NEVER:
       return kShelfAutoHideBehaviorNever;
     case SHELF_AUTO_HIDE_ALWAYS_HIDDEN:
-      // This one should not be a valid preference option for now. We only want
-      // to completely hide it when we run in app mode - or while we temporarily
+      // This should not be a valid preference option for now. We only want to
+      // completely hide it when we run in app mode - or while we temporarily
       // hide the shelf as part of an animation (e.g. the multi user change).
       return nullptr;
   }
   NOTREACHED();
   return nullptr;
 }
 
 }  // namespace
 
 const char kPinnedAppsPrefAppIDPath[] = "id";
@@ skipping 76 matching lines @@
   return AlignmentFromPref(GetPerDisplayPref(
       prefs, display_id, prefs::kShelfAlignmentLocal, prefs::kShelfAlignment));
 }
 
 void SetShelfAlignmentPref(PrefService* prefs,
                            int64_t display_id,
                            ShelfAlignment alignment) {
   DCHECK_GE(display_id, 0);
 
   const char* value = AlignmentToPref(alignment);
+  if (!value)
+    return;
+
   SetPerDisplayPref(prefs, display_id, prefs::kShelfAlignment, value);
   if (display_id == gfx::Screen::GetScreen()->GetPrimaryDisplay().id()) {
     // See comment in |kShelfAlignment| as to why we consider two prefs.
     prefs->SetString(prefs::kShelfAlignmentLocal, value);
     prefs->SetString(prefs::kShelfAlignment, value);
   }
 }
 
 }  // namespace ash