views: add Harmony dialog width support

ui/views/window/dialog_delegate.h

Index: ui/views/window/dialog_delegate.h
diff --git a/ui/views/window/dialog_delegate.h b/ui/views/window/dialog_delegate.h
index c74f5461ab9f131376a6261deb563a448be75c49..e83442cde091f918bee953526d12003d0477afdb 100644
--- a/ui/views/window/dialog_delegate.h
+++ b/ui/views/window/dialog_delegate.h
@@ -32,6 +32,13 @@ class LabelButton;
 class VIEWS_EXPORT DialogDelegate : public ui::DialogModel,
                                     public WidgetDelegate {
  public:
+  enum DialogWidth {
+    DIALOG_WIDTH_DEFAULT,
+    DIALOG_WIDTH_SMALL,
+    DIALOG_WIDTH_MEDIUM,
+    DIALOG_WIDTH_LARGE,
+  };
+
   DialogDelegate();
   ~DialogDelegate() override;
 
@@ -87,6 +94,11 @@ class VIEWS_EXPORT DialogDelegate : public ui::DialogModel,
   // the typical.
   virtual void UpdateButton(LabelButton* button, ui::DialogButton type);
 
+  // Returns the dialog width this dialog should use, or DIALOG_WIDTH_DEFAULT
+  // for the default width. This value is only honored when MD secondary UI is
+  // enabled.
+  virtual DialogWidth GetDialogWidth() const;
+
   // Overridden from ui::DialogModel:
   int GetDialogButtons() const override;
   int GetDefaultDialogButton() const override;
@@ -143,6 +155,7 @@ class VIEWS_EXPORT DialogDelegateView : public DialogDelegate,
   void GetAccessibleState(ui::AXViewState* state) override;
   void ViewHierarchyChanged(
       const ViewHierarchyChangedDetails& details) override;
+  gfx::Size GetPreferredSize() const override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(DialogDelegateView);