* Visibility widget

This attempts to address the confusion around how to hide a widget subtree.

* Apply review comments

* More clarifications

This includes the following changes :

e54bc4ea1 Fixed invalid call site of runWithEntrypointAndCallback (#5984)
764884b91 Removed callback for HeadlessDartRunner (#5983)
91537abba Revert "Temporarily add travis/analyze.sh back for Chrome bot (#5961)" (#5966)
3501acb70 Roll src/third_party/skia 9c9611fcc1bb..0d5d0659a684 (7 commits) (#5980)

Somehow I forgot to say "super.tap()" when calling "tap()" on the new
superclass, so it was just recursing infinitely but ended up actually
crashing on the first reuse of the finder.

The error was previously swallowed, I made this print it instead.

This fixes https://github.com/flutter/flutter/issues/18057

Add minOverscrollLength to make CupertinoScrollbar thumb correct size in long scroll views.

* update script

* Update update_icons.dart

* Update update_icons.dart

* Create test case for disabled state of outline button

Includes the following changes :
377793180 Roll Dart to version eab492385c3f345cb2f44f3b702b0e30e4a9c107 (#5979)
8a7af11f7 Fix IsolateStart event kind. (#5978)

Includes the following changes:
78f8bcace Annotate deprecated methods with @Deprecated (#5976)
4c7e5d5a1 Roll src/third_party/skia 0c5b0b1dd692..9c9611fcc1bb (13 commits) (#5977)
4208f8404 make ios text affinity behavior match android (#5971)
69b19a5f5 Roll src/third_party/skia f5402004c4a6..0c5b0b1dd692 (11 commits) (#5975)
8137d3411 Roll src/third_party/skia 4856f5fa596d..f5402004c4a6 (1 commits) (#5974)
cbe960d90 Roll src/third_party/skia 20714bdf90f3..4856f5fa596d (1 commits) (#5973)
f05a4ccaa Roll src/third_party/skia faeef7837210..20714bdf90f3 (11 commits) (#5970)
14af0348b Complete the AndroidView resize call only after a new frame is ready. (#5968)

Resizing an AndroidView happens asynchronously (as it requires thread
hopping from the ui thread to the platform thread).
While waiting for the resize to complete the framework does exactly when
the embedded view has been resized. This leads to pretty bad jank as the
framework might paint the embedded view with a wrong size.

We're working around this by freezing the texture frame while resizing
until we are sure that the next frame has the new size. This is how it
looks with the workaround:

This is how it looks before and after the workaround:

Before (janky) |  After (less janky)
:--------|---------:
![resize_before](https://user-images.githubusercontent.com/1024117/43669639-51bfd0ae-9739-11e8-8cbe-96e36f2460d2.gif) | ![resize_after](https://user-images.githubusercontent.com/1024117/43669647-62e885a6-9739-11e8-8aa4-beb74e979995.gif)

This depends on flutter/engine#5938. Additionaly right now the engine completes
the resize call immediately, a following PR will change it to complete
after a frame with the new size is ready.

* Roll engine to 7f083e54fe75

7f083e54f Don't implicitly fall through in switch statement (flutter/engine#5964)
c7ce6dd69 Apply translation to accessibility tree when in landscape (flutter/engine#5950)
aef94b73d Reland "Updated background execution implementation for Android" (flutter/engine#5954)
3421bca7a Roll src/third_party/skia 36216fb0acbc..177742435e52 (15 commits) (flutter/engine#5963)
9d1e67399 Temporarily add travis/analyze.sh back for Chrome bot (flutter/engine#5961)
4386afdaa Roll src/third_party/skia e6d0618f677c..36216fb0acbc (11 commits) (flutter/engine#5960)
7cef3da03 Roll src/third_party/skia 01d9a344b575..e6d0618f677c (1 commits) (flutter/engine#5958)
ad82cb154 Roll src/third_party/skia fdf05f4ff4e9..01d9a344b575 (1 commits) (flutter/engine#5957)
6ea410cfe Revert "Roll Dart to 17b54c76ce9b945c6f013ad08c19268409c0694a (flutter/engine#5955)" (#5956)
f20c58f65 Roll Dart to 17b54c76ce9b945c6f013ad08c19268409c0694a (flutter/engine#5955)
ed1938e99 Roll src/third_party/skia 641ac7daa81c..fdf05f4ff4e9 (3 commits) (flutter/engine#5953)
5f04e00d7 Remove travis directory (flutter/engine#5935)
5442c0a7d Revert "Updated background execution implementation for Android" (flutter/engine#5949)
a5215ce50 Add hasImplicitScrolling SemanticFlag and support in Android bridge (flutter/engine#5941)
4681351af Roll src/third_party/skia 6e487e67a3f3..641ac7daa81c (16 commits) (flutter/engine#5948)
bc885f319 Updated background execution implementation for Android
5770cbd2a Roll src/third_party/skia 12fb9cfeee07..6e487e67a3f3 (8 commits) (flutter/engine#5946)
f4464a8d9 Roll src/third_party/skia 2e77f54f46e8..12fb9cfeee07 (1 commits) (flutter/engine#5945)
c6baaaf75 Replace acquire+release thread annotation with excludes (flutter/engine#5944)
63ede2e35 Roll src/third_party/skia 59aabbcf3b0d..2e77f54f46e8 (1 commits) (flutter/engine#5943)
97aea093e Roll src/third_party/skia 71fe8baccc01..59aabbcf3b0d (1 commits) (flutter/engine#5942)
aaf4a9a24 Roll src/third_party/skia 4c3b63e289c5..71fe8baccc01 (3 commits) (flutter/engine#5940)

* Sync framework changes

This PR adds 2 features to RenderAndroidView and AndroidView:

1. Hit testing behavior
Adds a `PlatformViewHitTestBehavior` which is similar to
`HitTestBehavior` without the `deferToChild` option (as platform views
don't have child render objects) and with a `transparent` option which
prevents it from forwarding any events to the Android view.

2. MotionEvent recomposing logic
FlutterView and the framework `converter.dart` are working together to
transform each Android MotionEvent object into one or more
`PointerEvent` objects.

This PR adds the reverse logic (in _MotionEventDispatcher which is used
by RenderAndroidView) which turns a stream of PointerEvent objects into
MotionEvent objects.

The correctness of the recomposing logic is tested in an integration
test which will land in a separate PR (the unit test PR is pretty big,
trying to keep as many bite-size PRs for reviewer's convenience)

This removes the final traces of Travis and Appveyor from the Flutter tree.

I've updated the documentation and fixed a couple of places where scripts look for Travis, and eliminated the dart tools runningOnTravis function (which was unused anyhow).

There are places in the flutter script that used to look for the environment variable TRAVIS. We actually do want to continue to detect that we're running on Travis there, since in the plugins repo we still use Travis (for the moment). In any case, it's OK, because the CI environment variable is set on all of the CI bots (Cirrus, Travis, and Appveyor).

FastLane doesn't have a setup_cirrus equivalent to setup_travis, but it actually doesn't matter there either, since it doesn't do Travis-specific things, and it also looks for the CI environment variable.

Segment width now determined by width of widest child + children widgets now centered within segments

`run_recipe.py` has been removed and waterfall is deprecated...

* Refactor analysis benchmark and collect more data (#20169)

This does some code cleanup to avoid duplication, improves the logs,
and records min and max values as well as the mean.

* Fix typo that led to infinite loop

This switches docs and gallery build and deployment to use Cirrus CI instead of Travis, reapplying the changes from #19925, but updating the Firebase tokens for upload, and refining docs.sh some to limit retries to five times (instead of indefinitely).

* Enable lint unnecessary_statements. Codebase is compliant.

* Fix mega_gallery generated code to not generate unecessary statements

* Fix lint in mega gallery changes

* Enable unnecessary_statements for users as well as repo.

* Revert "increase size of user account drawer headers to 48 by 48 (#20266)"

This reverts commit 4a7b4a4d.

* Revert "EditableText Cursor can be set to not blink for testing (#20004)"

This reverts commit d041b319.

* Revert "Refactor analysis benchmark and collect more data (#20169)"

This reverts commit 5ea0a135.