webshare: Small refactor of WebShare (OnceCallback, const&, and alias)

chrome/browser/ui/browser_dialogs.h

Index: chrome/browser/ui/browser_dialogs.h
diff --git a/chrome/browser/ui/browser_dialogs.h b/chrome/browser/ui/browser_dialogs.h
index e82786079f6c931ae562f9a175afe233d9f37b7a..92c92d4da4595993d2196e83e3d4788341730dce 100644
--- a/chrome/browser/ui/browser_dialogs.h
+++ b/chrome/browser/ui/browser_dialogs.h
@@ -157,6 +157,11 @@ void ShowBookmarkEditorViews(gfx::NativeWindow parent_window,
 payments::PaymentRequestDialog* CreatePaymentRequestDialog(
     payments::PaymentRequest* request);
 
+// Used to return the target the user picked or nullopt if the user cancelled
+// the share.
+using WebShareTargetPickerCallback =
+    base::OnceCallback<void(const base::Optional<std::string>&)>;
+
 // Shows the dialog to choose a share target app. |targets| is a list of app
 // title and manifest URL pairs that will be shown in a list. If the user picks
 // a target, this calls |callback| with the manifest URL of the chosen target,
@@ -164,7 +169,7 @@ payments::PaymentRequestDialog* CreatePaymentRequestDialog(
 void ShowWebShareTargetPickerDialog(
     gfx::NativeWindow parent_window,
     const std::vector<std::pair<base::string16, GURL>>& targets,
-    const base::Callback<void(base::Optional<std::string>)>& callback);
+    WebShareTargetPickerCallback callback);
 
 #if defined(OS_MACOSX)