Consolidate two IsArcWindow functions to reduce code duplication

components/arc/arc_util.h

Index: components/arc/arc_util.h
diff --git a/components/arc/arc_util.h b/components/arc/arc_util.h
index a9e69d36878ecbaae809ccdd1c2cb6a630a5eed6..aa63bcbc324cc0382b03a51e1d5eb458b8fa9625 100644
--- a/components/arc/arc_util.h
+++ b/components/arc/arc_util.h
@@ -9,6 +9,10 @@
 // outside of ARC, e.g. CommandLine flag, attribute of global data/state,
 // users' preferences, and FeatureList.
 
+namespace aura {
+class Window;
+}  // namespace aura
+
 namespace base {
 class CommandLine;
 }  // namespace base
@@ -66,6 +70,10 @@ bool IsArcAllowedForActiveDirectoryUsers();
 // In most cases, it is disabled for testing purpose.
 bool IsArcOptInVerificationDisabled();
 
+// Returns true if the |window|'s aura::client::kAppType is ARC_APP. When
+// |window| is nullptr, returns false.
+bool IsArcAppWindow(aura::Window* window);
+
 }  // namespace arc
 
 #endif  // COMPONENTS_ARC_ARC_UTIL_H_