We've decided not to store the scroll position in PageStorage because
routes now maintainState by default.

Fixes #8051

The last remaining client is complex_layout.

They previously were very sensitive to widgets like LayoutBuilder.

These now test ScrollNotification2.

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