Allow resizable dialogs using BubbleFrameView to be resizable on Mac.
Allow resizable dialogs using BubbleFrameView to be resizable on Mac.

Dialogs such as BookmarkEditorView override WidgetDelegate::CanResize() to
return `true`. However, with the new dialog style, resizing is prevented by
the BubbleFrameView returning MaximumSize() := PreferredSize().

On Mac, windows/dialogs don't have or require resize handles, so everything
Just Works, once the MaximumSize() is plumbed through.

The BookmarkEdit dialog is resizable in Cocoa, so this allows the views
dialog to be consistent.

BUG=511051

Review URL: https://codereview.chromium.org/1287393003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#344098}

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