Switch SupportsUserData uses to use unique_ptr.

ios/chrome/browser/ui/dialogs/javascript_dialog_blocking_util.mm

Index: ios/chrome/browser/ui/dialogs/javascript_dialog_blocking_util.mm
diff --git a/ios/chrome/browser/ui/dialogs/javascript_dialog_blocking_util.mm b/ios/chrome/browser/ui/dialogs/javascript_dialog_blocking_util.mm
index 2acd84fcfde1c7c53c6a665eaaa3699f275aa8d6..c88c094f79b7a9ab2eb2f0461c93b685561e62ce 100644
--- a/ios/chrome/browser/ui/dialogs/javascript_dialog_blocking_util.mm
+++ b/ios/chrome/browser/ui/dialogs/javascript_dialog_blocking_util.mm
@@ -7,6 +7,7 @@
 #import <objc/runtime.h>
 
 #include "base/logging.h"
+#include "base/memory/ptr_util.h"
 #include "ios/web/public/web_state/web_state.h"
 #include "ios/web/public/web_state/web_state_observer.h"
 
@@ -53,7 +54,7 @@ class JavaScriptDialogBlockingStateWrapper
   explicit JavaScriptDialogBlockingStateWrapper(web::WebState* web_state)

[sdefresne, 2017/04/28 10:07:05]

Can you change this constructor to not take the web::WebState* and instead call
SetUserData in FromWebState:

  static JavaScriptDialogBlockingStateWrapper* FromWebState(
      web::WebState* web_state) {
    DCHECK(web_state);
    JavaScriptDialogBlockingStateWrapper* wrapper =
        static_cast<JavaScriptDialogBlockingStateWrapper*>(
            web_state->GetUserData(kBlockingStateKey));
    if (!wrapper) {
        wrapper = new JavaScriptDialogBlockingStateWrapper();
        web_state->SetUserData(kBlockingStateKey, base::WrapUnique(wrapper));
    }
    return wrapper;
  }

 private:
  JavaScriptDialogBlockingStateWrapper() = default;

       : state_(nullptr) {
     DCHECK(web_state);
-    web_state->SetUserData(kBlockingStateKey, this);
+    web_state->SetUserData(kBlockingStateKey, base::WrapUnique(this));
   }
 };