* Fix tests to use Ahem, and helpful changes around that

- Fix fonts that had metric-specific behaviours.

- LiveTestWidgetsFlutterBinding.allowAllFrames has been renamed
  to LiveTestWidgetsFlutterBinding.framePolicy.

- LiveTestWidgetsFlutterBinding now defaults to using a frame policy
  that pumps slightly more frames, to animate the pointer crosshairs.

- Added "flutter run --use-test-fonts" to enable Ahem on devices.

- Changed how idle() works to be more effective in live mode.

- Display the test name in live mode (unless ahem fonts are enabled).

- Added a toString to TextSelectionPoint.

- Style nit fixes.

* Roll engine to get Ahem changes.

* Update tests for dartdoc changes.

* Fix flutter_tools tests

Added a PluginRegistry to the new project template. The registry files will be automatically updated at build time to register the native plugins.

Fixes #7814.

* upgrade to linter-0.1.30

* add prefer_is_empty lint
* add directives_ordering lint
* add no_adjacent_strings_in_list lint
* add no_duplicate_case_values lint
* add prefer_collection_literals lint
* add prefer_const_constructors lint
* add prefer_contains lint
* add prefer_initializing_formals lint
* add unnecessary_null_aware_assignments lint
* add unnecessary_null_in_if_null_operators lint

This yak shave went as follows:

Fix https://github.com/flutter/flutter/issues/8795 by adding stocks to
the examples README.

Notice the layers entry in that README isn't quite right either.
Update that.

Check the layers/README file is worth pointing at.

Update the layers/README.

Let's run some of the layer tests to see if they still work.

Oops, need to update them to gradle.

Ok let's try running them again.

Oops, sector is broken.

Add a test for sector.

Fix sector. Find you need to add an assert to a const constructor.

Notice we need to turn const asserts on for the analyzer.

Notice the analysis_options files are out of sync with each other and
with the full list of lints.

Turn on the lints that should be on.

Fix the bugs that finds.

Xcode builds depend on the Python 'six' module. If not present, exit
immediately with a useful error message.

The six module is included in the system default Python installation. We
perform this check in case a custom Python install has higher priority
on $PATH; e.g., due to a Homebrew or MacPorts installation.

This extracts an existing doctor check to use it during the build step
as well.

The very first time `pod install` is invoked, CocoaPods downloads the master spec repository, which takes quite a while. Before this change, the build appeared to have stalled. With this change, at least the spinner is moving.

Added `pod setup` to the install instructions for CocoaPods, so the spec repo is downloaded while setting up Flutter, instead of during the first build.

Go through all packages brought in by pub, and write the name and path of every one that is a flutter plugin into .flutter-plugins.

In android/settings.gradle and ios/Podfile, read in .flutter-plugins, if that file exists. The Android / iOS code from the plugins is automatically added as dependencies of the native code of the app.

* Remove legacy .apk build.

Print out an error message telling the user to upgrade the project if
it's not Gradle-based. Removed all the obvious traces of the legacy
build.

Added support for Dart VM kernel snapshots in Gradle builds.

Fixed Android installs to verify that the app is actually installed, and
not just rely on the presence of the .sha1 file.

* Only run pod install if CocoaPods v1.0.0 or greater is installed.

Avoid issues with older versions of CocoaPods breaking the build. Users who genuinely use older versions of CocoaPods will have to run pod install manually when required.

1. Add `PortScanner` abstraction so that we don't do actual port scanning
   in tests.
2. Don't change the real `cwd` of the isolate during tests, as it affects
   all tests, not just the current running test.

Fixes #8761

(follow-on to #8698)

* Rename `Device.platform` to `Device.targetPlatform` to avoid
  collision with the exported variable from `platform.dart`

* Revert "Eliminate CocoaPods install step (#8694)"

This reverts commit f4a13bc7.

If the developer is relying on CocoaPods and hasn't done a pod install, we will do it for them. This is needed for a smooth native plugin experience, similar to what Gradle is doing on the Android side.

There's no hard dependency on CocoaPods. We only run pod install if the project uses CocoaPods, so developers are still free to use alternatives if they prefer (and if they don't want to use native plugins).

Fixes #8685
Fixes #8657
Fixes #8526

* Require CocoaPods 1.0.0 or newer.

And make sure we don't get a crash if running `pod install` fails.

* Address review feedback

This avoids unintentionally installing an older version if the
developer's homebrew installation is out-of-date.

The flutter tap was deleted as part of the resolution to #7783.

If the developer is relying on CocoaPods and hasn't done a pod install,
they'll get a build failure indicating the issue.

This also avoids a hard dependency on CocoaPods in the tool and allows
developers to customize their Xcode steps to use alternatives such as
Carthage if they prefer.

As of the latest Xcode versions, the latest published libimobiledevice
is out-of-date and build from HEAD is required.

This fixes two bugs:
1. Update initial install instructions to add --HEAD flag.
2. Update uninstall, reinstall instructions to include
   --ignore-dependencies flag, since other brew formulae depend on
   libimobiledevice.

Homebrew is an expected part of the iOS toolchain. Update the error
message to assume that.

This is consistent with the rest of the iOS toolchain.

Since iOS builds are CocoaPods enabled by default, we should make sure to run `pod install` to get pods wired up before building the app.

Also added a check to `flutter doctor` to verify CocoaPods is installed.

I'm passing FLUTTER_FRAMEWORK_DIR to the `pod install` command, so we can have the app's Podfile link in Flutter.framework as a pod instead of having to copy it over in xcode_backend.sh.

* Request the user upgrade if the Android SDK version is 24

* Update android_sdk_test.dart

* Update android_sdk.dart

* fix a doctor check for webstorm

* fix a missing reference

Only implemented for Android devices for now. Compare the installed SHA1
to the latest build. If they match, there's no reason to reinstall the
build.

Fixes #8295

Do not attempt to deploy/debug wifi connected iOS devices. ios-deploy is
able to install over wifi, but we've had several bugs reporting failure
to run/debug once installation has completed when the device is also
connected via USB. Note that we don't currently support deploy/debug
over wifi since libimobiledevice (which is also required) requires a USB
connection.

* Teach flutter tools to find gradle

Flutter tools will now use Gradle from Android Studio, which is now found automatically.

flutter doctor will verify that Android Studio has been installed, and that the included Gradle is at least version 2.14.1.

It is still possible to manually configure the path to Android Studio (flutter config --android-studio-dir=XXX) or Gradle (flutter config --gradle-dir=XXX), but this should only be necessary if they're installed somewhere non-standard.

Only tested on Linux and macOS for now.

Fixes #8131

Artifacts are now located in a central place.
This will enable us to downlaod artifacts when we need them (instead of
downloading them all upfront).
This also makes replacing sky_snapshot with gen_snapshot easier.