Rename defaultFocus to initialFocus.

packages/flutter/example/address_book/lib/main.dart

@@ -112,7 +112,7 @@ class AddressBookApp extends App {
         child: new TaskDescription(
           label: 'Address Book',
           child: new Focus(
-            defaultFocus: nameKey,
+            initialFocus: nameKey,
             child: buildMain()
           )
         )

packages/flutter/example/stocks/lib/stock_home.dart

@@ -322,7 +322,7 @@ class StockHome extends StatefulComponent {
     ];
     addMenuToOverlays(overlays);
     return new Focus(
-      defaultFocus: searchFieldKey,
+      initialFocus: searchFieldKey,
       child: new Stack(overlays)
     );
   }

packages/flutter/lib/widgets/focus.dart

@@ -14,17 +14,17 @@ class Focus extends Inherited {
 
   Focus({
     GlobalKey key,
-    GlobalKey defaultFocus,
+    GlobalKey initialFocus,
     Widget child
   }) : super(key: key, child: child);
 
-  GlobalKey defaultFocus;
+  GlobalKey initialFocus;
 
   GlobalKey _currentlyFocusedKey;
   GlobalKey get currentlyFocusedKey {
     if (_currentlyFocusedKey != null)
       return _currentlyFocusedKey;
-    return defaultFocus;
+    return initialFocus;
   }
   void set currentlyFocusedKey(GlobalKey value) {
     if (value != _currentlyFocusedKey) {