Use active window if on current workspace for fullscreen mode.

ash/switchable_windows.h

Index: ash/switchable_windows.h
diff --git a/ash/switchable_windows.h b/ash/switchable_windows.h
index 305921bf662cc02c34d80d997002dfd0185083e4..b0b4ee0178bf12beba0263ec218e77057cd3423a 100644
--- a/ash/switchable_windows.h
+++ b/ash/switchable_windows.h
@@ -8,6 +8,10 @@
 #include "ash/ash_export.h"
 #include "base/macros.h"
 
+namespace aura {
+  class Window;
+}
+
 namespace ash {
 
 // List of containers which contain windows that can be switched via Alt+Tab to.
@@ -16,6 +20,9 @@ ASH_EXPORT extern const int kSwitchableWindowContainerIds[];
 // The number of elements in kSwitchableWindowContainerIds.
 ASH_EXPORT extern const size_t kSwitchableWindowContainerIdsLength;
 
+// Returns true if |window| is a container for windows which can be switched to.
+ASH_EXPORT bool IsSwitchableContainer(const aura::Window* window);
+
 }  // namespace ash
 
 #endif  // ASH_SWITCHABLE_WINDOWS_H_