Implement a modal permission dialog on Android gated by a feature.

chrome/browser/permissions/permission_infobar_delegate.h

Index: chrome/browser/permissions/permission_infobar_delegate.h
diff --git a/chrome/browser/permissions/permission_infobar_delegate.h b/chrome/browser/permissions/permission_infobar_delegate.h
index 6f2ef7940e4fbb74d9dbe71907d94e420fe53481..f2ea4b4970c68192503e08e33cabc803f34fd6d9 100644
--- a/chrome/browser/permissions/permission_infobar_delegate.h
+++ b/chrome/browser/permissions/permission_infobar_delegate.h
@@ -23,12 +23,17 @@ class InfoBar;
 class InfoBarService;
 class Profile;
 
-// Base class for permission infobars, it implements the default behavior
-// so that the accept/deny buttons grant/deny the relevant permission.
-// A basic implementor only needs to implement the methods that
+// Base delegate class for permission prompts on Android. The default behavior
+// is that the accept/deny buttons grant/deny the relevant permission
+// respectively. A basic implementor only needs to implement the methods that
 // provide an icon and a message text to the infobar.
+//
+// By default, the user is presented with an infobar to make their choice. If
+// the experimental ModalPermissionPrompts feature is active, they will instead
+// see a modal dialog. Currently, this class is used for both; future
+// refactoring will be undertaken based on whether support for infobars is
+// retained following the modal prompt experiment.
 class PermissionInfoBarDelegate : public ConfirmInfoBarDelegate {
-
  public:
   using PermissionSetCallback = base::Callback<void(bool, PermissionAction)>;
 
@@ -55,6 +60,10 @@ class PermissionInfoBarDelegate : public ConfirmInfoBarDelegate {
   bool persist() const { return persist_; }
 
   // ConfirmInfoBarDelegate:
+  bool Accept() override;
+  bool Cancel() override;
+  void InfoBarDismissed() override;
+  base::string16 GetButtonLabel(InfoBarButton button) const override;
   base::string16 GetMessageText() const override;
 
  protected:
@@ -68,11 +77,7 @@ class PermissionInfoBarDelegate : public ConfirmInfoBarDelegate {
  private:
   // ConfirmInfoBarDelegate:
   Type GetInfoBarType() const override;
-  void InfoBarDismissed() override;
   PermissionInfoBarDelegate* AsPermissionInfoBarDelegate() override;
-  base::string16 GetButtonLabel(InfoBarButton button) const override;
-  bool Accept() override;
-  bool Cancel() override;
 
   virtual int GetMessageResourceId() const = 0;
   void SetPermission(bool update_content_setting, PermissionAction decision);