Checksum validation is intended only as a performance improvement.
Checksum de-serialization errors (typically framework version mismatch) are
expected on framework updates and shouldn't be user-visible except for
informational purposes when --verbose is set.

Adds the app entrypoint as a key in the checksum file.

This change eliminates the assumption that checksummed files change when
the main entrypoint changes. In the case where there are two
entrypoints, a.dart and b.dart and a.dart imports b.dart and b.dart
imports a.dart, building the app with entrypoint a.dart followed by a
build of the app with entrypoint b.dart would result in the same
files list and checksums, but should invalidate the build.

Extract a Snapshotter class that can be shared between FLX snapshotting,
AOT snapshotting, and assembly AOT snapshotting. Allows for better
testability of snapshotting logic.

* Extracts script snapshotting used in FLX build.
* Adds tests for snapshot checksumming, build invalidation/skipping.

Remaining work: disentangle + extract AOT snapshotting and Assembly AOT
snapshotting logic from build_aot.dart.

This change re-introduces skipping AOT snapshot builds if input sources
and outputs have not changed since the last snapshot build, assuming a
build for the same platform in the same build mode.

This reverts commit 3d5afb5a.
It includes the following changes relative to the original:
  1. Include the entrypoint source in the checksums
  2. include the build mode in the checksums
  3. include the target platform in the checksums

This change ensures that snapshot build checksums used to avoid
duplicate builds are invalidated by a change to framework revision
(in case gen_snapshot is updated), as well as by build mode.

Currently, only FLX snapshotting uses checksums to avoid duplicate
builds. FLX snapshotting is always done with BuildMode.debug, so didn't
include build mode in the checksum file.

This reverts commit 1705bf3c.

* Revert "Fix a typo in the saved certificate error message (#11640)"

This reverts commit bfda885a.

* Revert "Rollback patch that broke microbenchmarks (#11616)"

This reverts commit 70fe6f4c.

* Revert "Extract snapshotting logic to Snapshotter class (#11591)"

This reverts commit 309a2d78.

* Revert "Minor whitespace formatting fix (#11590)"

This reverts commit bf69c3c6.

* Revert "Avoid rebuilding snapshots if no change to source (#11551)"

This reverts commit 74835db5.

First step in eliminating code duplication between script snapshotting
(in FLX build) and AOT, assembly AOT snapshotting.

This change re-introduces skipping snapshot builds if input sources (and
outputs) have not changed since the last snapshot build, with a bugfix
to include the entry-point source in the checksum used to check whether
rebuild can be skipped. This ensures that the following sequence
invalidates the cached build, resulting in two snapshot builds:

  flutter build ios lib/foo.dart
  flutter build ios lib/bar.dart

This reverts commit 3d5afb5a.

* Revert "Support space- and backslash-escaped dependencies (#11090)"

This reverts commit e6bafd0b.

* Revert "Skip AOT snapshot build if inputs are unchanged (#11084)"

This reverts commit b5e522e2.

* perform the initial poll for devices quicker

* add a Poller class

* test the new Poller class

* pass the value of the android sdk

* swap flag

* allow the user to set the android-sdk location

* Include the process' `stdout` and `stderr` when it returns a
  non-zero exit code in `runCheckedAsync()`
* Defensively catch errors in `AndroidDevice.isAppInstalled()`
  and return false

* minor tweaks to the output for flutter_tools

* update test expectations

Snapshot dependency files now backslash-escape dependency paths
containing spaces and backslashes.

See: https://codereview.chromium.org/2966903003/

Previously, the snapshot file was recomputed on every build. We now
record checksums for all snapshot inputs (which are catalogued in the
snapshot dependencies file output alongside the snapshot) and only
rebuild if the checksum for any input file (or the previous output file) has
changed.

Previously, the snapshot file was recomputed on every build. We now
record checksums for all snapshot inputs (which are catalogued in the
snapshot dependencies file output alongside the snapshot) and only
rebuild if the checksum for any input file has changed.

* add min version checks for IntelliJ

* validate the installed versions of IntelliJ and the flutter plugin

* review comments

* Let run default to first profile

* fix

* review notes

* first pass

* improvements

* extract terminal.dart

* rebase

* add default terminal to context

* The analyzer wants the ../ imports in front of the ./ imports

* review notes

Rather than complain about these in a code review I figured I'd just fix them. :-)

This way, you can test things even with a VerboseLogger.

Add a flutter doctor --android-licenses command that locates and runs the Android SDK license manager (#9892)

See https://github.com/flutter/flutter/issues/8438

Eagerly generate local.properties, and always update the flutter.sdk
setting in it, in case FLUTTER_ROOT has changed.

Fixes #8365.
Fixes #9716 - at least the specific issue reported. My Android Studio
still complains about Gradle versions - it ships with v3.2, but requires
v3.3...

Add a 'generate dependencies' task to the Gradle build, which checks if
the snapshot dependencies file exists, and runs an extra build before
the actual FlutterTask if it doesn't. This makes the first build slower,
but sub-sequent builds (without source changes) much faster.

Fixes #9717.

* Let printError print bold as well

* review notes

* Populate PUB_ENVIRONMENT for initial pub get

* review comments

* change order

FlutterCommand.runCommand subclasses can optionally return a FlutterCommandResult which is used to append additional analytics. 

Fix flutter run timing report and add a bunch of dimensional data

Note: In a cross-platform context `Uri.path` is not a valid file path. Allways use `fs.path.fromUri` to convert.

`adb` can sometimes hang, which will in turn hang the Dart isolate if
we're using `Process.runSync()`. This changes many of the `Device` methods
to return `Future<T>` in order to allow them to use the async process
methods. A future change will add timeouts to the associated calls so
that we can properly alert the user to the hung `adb` process.

This is work towards #7102, #9567

* Do not lower-case paths during canonicalization.

This breaks hot reload on some platfroms with case insensitive file systems.

* Add unit tests