This reverts commit 4caa68b8.

This reverts the previous roll to 33397f which included an assertion we ended up tripping over on certain scenes. A Skia issue has been filed for this https://bugs.chromium.org/p/skia/issues/detail?id=7225.

The hermetic Xcode tooling in that repo is not yet easily usable for
Xcode 9. There are two main issues:

1. The tooling currently assumes that macOS host builds should use
   Xcode 8, whereas iOS builds should use Xcode 9. Flutter builds should
   use Xcode 9 in all cases.
2. The tooling currently includes a bail-out condition for iOS builds
   that exits non-zero immediately (Chrome hasn't yet migrated its iOS
   build to this tooling).

In the meantime, I've manually updated the bot infra with Xcode 9 and
we'll continue to use the current find_xcode.py tooling until Chrome's
new Mac/iOS tooling is ready.

* Roll dart to pick up fix for diagnostic server

* Fix runUnaryGuarded, runBinaryGuarded calls

* Revert changes to runUnaryGuarded, runBinaryGuarded as they seem to be local-only, perhaps dependent on version of analyzer

* Update third_party license hash. No changes to licenses

* Add dependency on chromium/src/build for Mac/iOS build

Preparation for migrating to mac_toolchain.py for installing/configuring
Xcode versions on the Mac build bots.

* Exclude third_party/chromium_build from licence script

It's used only at build time to fetch and install the correct Xcode
version.

* Roll dart to 87538ffd7eca3405d13e46dcf3a20dcdcde9761e

* Update license hash

Revert "Revert "Roll dart to pick up change where platform.dill was removed (#4180)" (#4185)" (#4186)

This reverts commit a89f4669.

Doing the synchronized roll of Dart into engine as well as into Fuchsia
to prevent Fuchsia breakage.

This reverts commit 37f571ee.

* Roll dart to pick up change where platform.dill was removed

* Fix flutter patch sdk generation

* Update license hash. No changes to license text.

* Roll dart to pick up a fix for zero-rebuild problem

* Update license hash

* Switch from FlutterFastaTarget to FlutterTarget as FlutterFastaTarget was removed.

This reverts commit 0d2f0cb6.

Attempting to roll into the framework causes analysis errors with
mock classes implementing HTTP-related classes previously in dart:io:
[error] Classes can only implement other classes. (packages/flutter_tools/test/base/net_test.dart, line 94, col 41)
[error] Classes can only implement other classes. (packages/flutter_tools/test/base/net_test.dart, line 62, col 33)
[error] Classes can only implement other classes. (packages/flutter_tools/test/base/net_test.dart, line 78, col 40)
[error] Classes can only implement other classes. (packages/flutter_tools/test/src/context.dart, line 249, col 46)

and dartdoc failures:
dartdoc:stdout: [error] Target of URI doesn't exist: 'dart:_http'. at /home/travis/build/flutter/flutter/bin/cache/pkg/sky_engine/lib/io/io.dart, line 206.

* Revert "libtxt: handle characters encoded as multiple UTF-16 code units (#4165)"

This reverts commit 414c3fe3.

* Revert "Proper horizontal a11y scrolling on Android (#4163)"

This reverts commit 0448bf9b.

* Revert "Update Skia revision to 74a8296d7c. (#4164)"

This reverts commit ac53d29a.

* Revert "Revert "Revert engine Dart roll. (#4158)" (#4162)"

This reverts commit f97e974e.

This reverts commit 14aab33e.

e1aa8673 fixes issue with last dart
roll.

* Revert "Include _http into sky_engine libraries for analyzer (#4154)"

This reverts commit b930f107.

It is dependent upon the Dart roll, which breaks the engine.

* Revert "Roll dart to ade37f931e90b0fdb8fe16d6bf6f089545da55b6 (#4151)"

This reverts commit 6f1264fb.

This Dart roll breaks the engine build on Travis.

* Roll dart

* Update dart dependencies

* Update dart license hash. No changes to licenses

* Roll to one more version up

* Update license hash

This reverts commit 513828b5.

This breaks linux build due to outdated pool dependency in observatory pub packages.

* Roll dart dependency to 24ad1035147b65dd42e765b566f5002e87caafa7

* Update dart license hash(no relevant changes). Update dart deps.

* Revert "Roll Dart to 3d21a46b726c24ded2d3cb3cce4f43aeed875dbc. (#4127)"

This reverts commit 321e639b.

* Revert "Roll skia to 76d640d14ea78e1f827a2f545e7f0729cdc2896f (#4129)"

This reverts commit 6aaba3d2.