Changed DefaultTextStyle to consider the TextTheme defined in the context for Bottom Nav Bar (#7042)

* Changed DefaultTextStyle to consider the TextTheme defined in the context

* added regression test for bottom nav bar text themes

* added second regression test for fixed navbar

Fixes https://github.com/flutter/flutter/issues/6947

With this change, they're run via instance methods on an object
obtained through the context. This will allow us to substitute
that object in tests with replay/record versions to allow us to
mock out the os-layer in tests.

* Skip failing input tests

* Only skip on Mac OS

Started failing at 0b737ac5.

https://github.com/flutter/flutter/commit/737a55ef3e47036220e72f3b3e17353d461b5fab

This Fuchsia-specific code is moving into Fuchsia itself.

Returns a dump of the application's render tree.

because this is the most full-featured sample we have.

This fixes minor issues I ran into while using Flutter.

These now match what 2016.3 expects.

Q: What happens if we set time dilation to zero?
A: It would be bad.

@hixie told me to add me to the list, see https://github.com/flutter/flutter/pull/6833#issuecomment-260418501

Fixes #5695

* Fixes Analysis Server regression (https://github.com/dart-lang/sdk/issues/27856).
* Adds `front_end` dependency override (required by analyzer).