Move Singleton and related structs to namespace base

ui/views/accessibility/native_view_accessibility_auralinux.cc

Index: ui/views/accessibility/native_view_accessibility_auralinux.cc
diff --git a/ui/views/accessibility/native_view_accessibility_auralinux.cc b/ui/views/accessibility/native_view_accessibility_auralinux.cc
index 37c43bb7c8ca770cfa5d26b8300ccf02b48bcc6c..a0900c17329c8df05d704e5efe22a1f7d03b06ba 100644
--- a/ui/views/accessibility/native_view_accessibility_auralinux.cc
+++ b/ui/views/accessibility/native_view_accessibility_auralinux.cc
@@ -33,7 +33,7 @@ class AuraLinuxApplication
  public:
   // Get the single instance of this class.
   static AuraLinuxApplication* GetInstance() {
-    return Singleton<AuraLinuxApplication>::get();
+    return base::Singleton<AuraLinuxApplication>::get();
   }
 
   // Called every time we create a new accessibility on a View.
@@ -114,7 +114,7 @@ class AuraLinuxApplication
   }
 
  private:
-  friend struct DefaultSingletonTraits<AuraLinuxApplication>;
+  friend struct base::DefaultSingletonTraits<AuraLinuxApplication>;
 
   AuraLinuxApplication()
       : platform_node_(ui::AXPlatformNode::Create(this)) {