Replace version-specific link with a version-independent URL.

See https://github.com/flutter/flutter/issues/7579

This used to be the logic before I made the tests portable.

Fixes https://github.com/flutter/flutter/issues/7974

* Make new project template gradle-based for Android.

With this change, the 'new project' template uses the same gradle-based build for Android as the hello_services example. This has some implications on build performance, since we're now building a complete Android app instead of just combining a pre-compiled .dex with the Flutter assets.

The very first build is a little over 2x slower, since it needs to download gradle and build the build scripts before getting to the actual code. Subsequent builds with changes to the code are comparable to the old builds. Null builds are faster. Enabling the gradle daemon speeds up subsequent builds by around 5s.

* Move Flutter Gradle plugin to Flutter root.

Having the drawer docs lead with "this is a drawer" wasn't very
helpful when scanning.

qv. study P6.

Fixes https://github.com/flutter/flutter/issues/7963

Required to support Flutter SDK paths with spaces.

Required to handle Flutter SDK (and other) paths that include spaces.

Also includes general cleanup:
* Declare explicitly that we use /bin/bash, since we rely on its
  features.
* Add -- where possible, to avoid interpreting files starting in - as
  options.
* Suppress output of pushd/popd.
* Avoid stringifying arrays.

We call the builder in slightly different ways, but the new results
seem reasonable.

* Support changing the dismissable threshold for any direction for dismissable widget.

* Fixing review comments.

All the clients have migrated to GridView.  Also, remove RenderGrid,
which isn't needed by GridView.

* return 1 when checks in `flutter.bat` fail
* don't assume file extension of git (depending on the system it can be `git.exe` or `git.bat`)

* Sync CONTRIBUTING.md text with engine.git

Turns out we had very similar text in engine.git.  This patch makes the text the same by adopting the text in engine.git.

* Update CONTRIBUTING.md

We weren't triggering a relayout when the number of children changed.

Fixes #8001

* Fix potential NPE in iOS doctor check

In case Xcode is not installed, the xcode-select path may be null.

* fixup! Fix potential NPE in iOS doctor check

If the developer has only installed the Xcode command-line tools,
xcode-select and some other tools may be present, but xcodebuild will be
missing. In this case, output a slightly improved message indicating
that the installation is incomplete rather than missing.

* Add indent option to logger and indent non-flutter nested output

* Add a missed override

* Formatting

Move the back button and drawer opening logic into the app bar.

Move the tap-status-bar-to-scroll-to-top logic to using
ScrollControllers. Provide a PrimaryScrollController and a `primary`
flag on scroll views.

Make it possible to track when a route becomes or stops being poppable.

* Allow for customization of hintText in InputField

* Adding tests.

* disables all `flutter test` and `flutter drive` tests on Windows as those two commands are not fully implemented on Windows yet
* fixes other failures on Windows