Double clicking the resize handle should expand window along that axis.

ui/aura/test/test_window_delegate.cc

Index: ui/aura/test/test_window_delegate.cc
===================================================================
--- ui/aura/test/test_window_delegate.cc	(revision 124527)
+++ ui/aura/test/test_window_delegate.cc	(working copy)
@@ -16,7 +16,7 @@
 ////////////////////////////////////////////////////////////////////////////////
 // TestWindowDelegate
 
-TestWindowDelegate::TestWindowDelegate() {
+TestWindowDelegate::TestWindowDelegate() : window_component_(HTCLIENT) {
 }
 
 TestWindowDelegate::~TestWindowDelegate() {
@@ -45,7 +45,7 @@
 }
 
 int TestWindowDelegate::GetNonClientComponent(const gfx::Point& point) const {
-  return HTCLIENT;
+  return window_component_;
 }
 
 bool TestWindowDelegate::OnMouseEvent(MouseEvent* event) {