Fix two failing tests

This fixes the following tests that seem to have become broken with the removal of global CSS from AT:

```
test.aria.widgets.container.dialog.resize.test3.DialogOnResizeTestCase
test.aria.widgets.container.tooltip.TooltipTestCase
```

They relied on derivatives of font size for assertions.

It also adds possibility for TemplateTestCase and FrameATLoader to pass the CSS to be injected into the iframe's `<body>` inline CSS.