* Remove SHA1 check from AndroidDevice.isAppInstalled()

The docs for isAppInstalled say 'check if a version of the given app is
already installed', however the current code returns true only if it's
the latest build that's installed.

This made sense in the past, when the use pattern was:

  if (!isAppInstalled(...)) installApp(...);

but now the usage is:

  if (isAppInstalled(...)) uninstallApp(...);
  installApp(...);

This has the probably unintended consequence that if you run `flutter
install` or `flutter run` two times in a row with no source changes, the
second invocation will uninstall the app, but the first invocation might
not.

Removing the SHA1 check makes us always uninstall the app if it's
installed.

Fixes #8172

Finally found the command to run tests in checked mode on my system. This one should've been caught by the IDE, but wasn't.

* 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

When resizing a PageView from 0x0, we weren't sure what the old page
number was because all the pages are collapsed at zero. Now we avoid the
divide by zero and default to the initialPage.

Fixes #8285

Previously, we were dividing by zero.

Fixes #8281

Also, make all painters have a toString by default.

Now that all the breaking scrolling changes are in, this seems like a reasonble
time to rev package:flutter's version number.

Rename all the "2" classes related to scrolling to remove the "2". Now that the
old scrolling code is gone, we don't need to use the suffix.

* Do not attempt to merge non-fat frameworks in Xcode build

During the Xcode build, we strip code irrelevant to the target
architecture in frameworks used by the application. In the case of
non-fat executables, no stripping occurs, so the frameworks can be used
as-is. No merge & replace step is necessary.

* fixup! Do not attempt to merge non-fat frameworks in Xcode build

* More better toStrings and more vigorous smoke testing of gallery

* Update scroll_controller.dart

* Update sliver.dart

* Add --start-paused doc

* correcting > Observatory

* Updating --start-paused option w/feedback

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.

Also: Fix some analyzer warnings.

* Support iOS screenshot 1/3

* Use path.join

* use fs.path instead

Fixes https://github.com/flutter/flutter/issues/5935

* ups pinned `test` to `0.12.15+9` (to play nice w/ the latest analyzer)
* integrates `analyzer` with analysis driver defaulting to ON

Fixes #8209

All the clients have migrated to Scrollable2.

Update stack_trace_test.dart for changes to the naming of async body functions.

This does not attempt to correct any logic, only to port it as written.

The API changed a bit to take into account what is newly available and
no longer available in the new world.

* Enable Gradle Workflow on Windows

With this the app created by `flutter create` now compiles on Windows.

* Move OS check to gradle file

* Move simulator screenshot logic to use simctl

* Add simulator screenshot tests

- ScrollableList
 - ScrollableLazyList
 - LazyBlock
 - MaterialList

Clients should use ListView instead.

Previously, the scroll correction code path was untested. This patch
introduces a test for the code path and fixes two issues with it.
There's likely more work we'll need to do in this area to nail down all
the cases.

Fixes #8155

This assumes a fix to https://github.com/dart-lang/test/issues/542

The timeout added in this patch is a workaround for https://github.com/dart-lang/coverage/issues/165

This reverts commit fac9efba.

The timeout was fixed by 6795c4ab.