WIP (Introduce WTF::NonNullPtr<T>.)

Source/core/page/FocusController.cpp

Index: Source/core/page/FocusController.cpp
diff --git a/Source/core/page/FocusController.cpp b/Source/core/page/FocusController.cpp
index 81c41299e3ac4f938a8a89c010407ded93afb22a..6300c61ce16065eeebdacc8c4963c14de270a6fb 100644
--- a/Source/core/page/FocusController.cpp
+++ b/Source/core/page/FocusController.cpp
@@ -63,10 +63,9 @@ using namespace HTMLNames;
 
 // FIXME: Some of Node* return values and Node* arguments should be Element*.
 
-FocusNavigationScope::FocusNavigationScope(TreeScope* treeScope)
+FocusNavigationScope::FocusNavigationScope(NonNullPtr<TreeScope> treeScope)
     : m_rootTreeScope(treeScope)
 {
-    ASSERT(treeScope);
 }
 
 Node* FocusNavigationScope::rootNode() const
@@ -94,7 +93,7 @@ FocusNavigationScope FocusNavigationScope::focusNavigationScopeOf(Node* node)
         root = n;
     // The result is not always a ShadowRoot nor a DocumentNode since
     // a starting node is in an orphaned tree in composed shadow tree.
-    return FocusNavigationScope(&root->treeScope());
+    return FocusNavigationScope(root->treeScope());
 }
 
 FocusNavigationScope FocusNavigationScope::ownedByNonFocusableFocusScopeOwner(Node* node)