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.

This reverts commit 59bb2dba.

This reverts commit 0f557e72.

This reverts commit dac1baf4.

* Revert "New Flutter Gallery UI (#16936)"

This reverts commit 7038597b.

A new front-end for the Flutter Gallery example.

* android templates should add density and screenLayout to config changes

* update the rest of the manifests

* iOS works

* Works on Android

* Take in commit number in iOS also. Get rid of image upload for Android. It's just a waste of bandwidth

* Tweak to fix on Travis

* first round fastlane working on Android

* clean up and start ios

* Partial iOS

* Got a fastfile that works on iOS

* Finalize Android push instructions

* Finalize instructions for iOS

* Extra cleanup and optipng

* Disable readme autogen and add a default readme

This reverts commit 36e3b103 to make the build green.

This reverts commit 25b1d43a.

This reverts commit 05d6b08f.

This consolidates all of the non-template .gitignore rules into the top level .gitignore, to ignore common things more broadly, with less maintenance needed for the .gitignore files. Does not touch the templates, so that they still produce needed .gitignores as part of flutter create.

* Add framework-side support for system text scale factor.

* Rolling engine to e3404b81a53ba3180c7623a6f2190ebb28518f30
  Additional changes rolled in with engine change:
    libtxt: implementation of GetRectsForRange that processes a line at a time - e3404b8
    Provide an entropy source to the Dart engine (#4161) - e1aa867
    libtxt: search for fallback fonts that can match emoji and CJK characters - 8061df1
    Roll skia to e4679fa06a. (#4157) - 267e7a8
    Update buildroot to 53fea9aebbcc39c6522731471a1a45960ee0685e (#4160) - 02ea7ae
    Revert engine Dart roll. (#4158) - 14aab33
    Add support for system text scale factor. (#4124) - b2a7f4b
    Include _http into sky_engine libraries for analyzer (#4154) - b930f10
    libtxt: Remove postprocess_line and improve tracking of X offsets - 86f95f0
    libtxt: remove redundant line_widths (#4152) - 14bf515
    Roll dart to ade37f931e90b0fdb8fe16d6bf6f089545da55b6 (#4151) - 6f1264f

* add Android instrumentation test

* add devicelab test

* add to manifest.yaml

* rename _smoke_test.dart to _smoketest.dart to prevent flutter test from picking it up

* volatile fields; style fixes

* use ConditionVariable; fix sh script

Under android/ directory, ignore:
GeneratedPluginRegistrant.java

Under ios/ directory, ignore:
GeneratedPluginRegistrant.h
GeneratedPluginRegistrant.m
Pods/

* Roll android build tools to 25.0.3

* Roll android build tools to 25.0.3 in templates