Adding a way to associate Android Activities with PlatformWindowAndroid

ui/aura/client/aura_constants.h

Index: ui/aura/client/aura_constants.h
diff --git a/ui/aura/client/aura_constants.h b/ui/aura/client/aura_constants.h
index 5999b850978c4f64c533ad574982aedddf71d6de..71afa7a9c59b03f5b39bc5d6624714b9571248f3 100644
--- a/ui/aura/client/aura_constants.h
+++ b/ui/aura/client/aura_constants.h
@@ -9,6 +9,10 @@
 #include "ui/aura/window.h"
 #include "ui/base/ui_base_types.h"
 
+#if defined(OS_ANDROID)
+class JavaObjectWeakGlobalRef;
+#endif
+
 namespace ui {
 class InputMethod;
 }
@@ -18,6 +22,12 @@ namespace client {
 
 // Alphabetical sort.
 
+#if defined(OS_ANDROID)
+// A property key to store Android Activity associated with the root window.
+AURA_EXPORT extern const WindowProperty<JavaObjectWeakGlobalRef*>* const
+    kActivityForRootWindow;
+#endif
+
 // A property key to store always-on-top flag.
 AURA_EXPORT extern const WindowProperty<bool>* const kAlwaysOnTopKey;