Use active window if on current workspace for fullscreen mode.

ash/switchable_windows.cc

Index: ash/switchable_windows.cc
diff --git a/ash/switchable_windows.cc b/ash/switchable_windows.cc
index 86c31f66e335d7b08b5212f3d5ca5ff574794510..352599b250a29a2332b39be5031aba798255636d 100644
--- a/ash/switchable_windows.cc
+++ b/ash/switchable_windows.cc
@@ -5,6 +5,7 @@
 #include "ash/switchable_windows.h"
 
 #include "ash/shell_window_ids.h"
+#include "ui/aura/window.h"
 
 namespace ash {
 
@@ -17,4 +18,14 @@ const int kSwitchableWindowContainerIds[] = {
 const size_t kSwitchableWindowContainerIdsLength =
     arraysize(kSwitchableWindowContainerIds);
 
+bool IsSwitchableContainer(const aura::Window* window) {
+  if (!window)
+    return false;
+  for (size_t i = 0; i < kSwitchableWindowContainerIdsLength; ++i) {
+    if (window->id() == kSwitchableWindowContainerIds[i])
+      return true;
+  }
+  return false;
+}
+
 }  // namespace ash