* fix Curves.bounceInOut

* assert maximum slope

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

Enables animated curve diagrams in the documentation, replacing the static images.

It was causing problems rolling Flutter into Fuchsia

* re-enable lint unnecessary_const

* remove trailling whitespaces

* remove unnecessary const (after merge)

This reverts commit cc1cf13e.

Our style guide says the k's are not necessary, and it seems like a good idea to make all the code be consistent on this.

Only naming changes to private vars: no logic changes.

I'm moving the assets in the assets-for-api-docs repo to a slightly different location to help with organization in that repo, so this PR points the doc URLs to the new location. The old assets won't be removed until this PR makes its way to the API docs website.

No documentation or code changes here, other than changing doc image URLs.

I got tired of drive-by spelling fixes, so I figured I'd just take care of them all at once.

This only corrects errors in the dartdocs, not regular comments, and I skipped any sample code in the dartdocs. It doesn't touch any identifiers in the dartdocs either. No code changes, just comments.

Turns out we have many immutable classes.

Fixes #6892

Covers lib/ in package:flutter.

Port DecelerateInterpolator to Flutter.

Also, hide the Curve subclasses that you can't extend and that have no
statics and are generally not useful.

For consistency with Tween.

Fixes #5169

In the interest of using the name in the case of Material steppers,
this commit renames Step curve to Threshold.

We should center the title of flexible space bars on iOS.

Related to #4962

Everything now has dartdocs except one setter whose getter already has
docs.

Fixes #617

As usual, as I was doing this I ran into some stuff that seemed hard
to document as-is and so I changed it. In this case, in the "http"
library. The new code is more or less equivalent, I think, but the
resulting documentation makes it more obvious that it's wrong...

For those times when you want to do something as you move away from a
route into the next one, as well as when you move into it from the
previous one.

This patch simplifies AnimationTiming and all the AnimatedValue base classes.
Also, make PopupMenu a stateless component because it has no state.

Fixes #1168