[ObjC ARC] Converts ios/chrome/browser/ui/contextual_search:contextual_search to ARC.

ios/chrome/browser/ui/contextual_search/window_gesture_observer.mm

Index: ios/chrome/browser/ui/contextual_search/window_gesture_observer.mm
diff --git a/ios/chrome/browser/ui/contextual_search/window_gesture_observer.mm b/ios/chrome/browser/ui/contextual_search/window_gesture_observer.mm
index 0ef504e8114087cc42992b25b0d97e3076c5df6c..9a89c05732f20c69af9ae1302bd77e6d21fb0a53 100644
--- a/ios/chrome/browser/ui/contextual_search/window_gesture_observer.mm
+++ b/ios/chrome/browser/ui/contextual_search/window_gesture_observer.mm
@@ -4,6 +4,10 @@
 
 #include "ios/chrome/browser/ui/contextual_search/window_gesture_observer.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 @implementation WindowGestureObserver {
   NSObject* _target;
   SEL _action;
@@ -42,11 +46,16 @@
     if (![[touch view] isDescendantOfView:_viewToExclude]) {
       _touchedView = [touch view];
       dispatch_async(dispatch_get_main_queue(), ^{
+
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
         if (_actionPassesSelf) {
           [_target performSelector:_action withObject:self];
         } else {
           [_target performSelector:_action];
         }
+#pragma clang diagnostic pop
+
       });
       // Only invoke from the first qualifying touch.
       break;