* add key to constructors of public widgets

* fix a test

* fix a test

This reverts commit c235998a.

* Update project.pbxproj files to say Flutter rather than Chromium

Also, the templates now have an empty organization so that we don't cause people to give their apps a Flutter copyright.

* Update the copyright notice checker to require a standard notice on all files

* Update copyrights on Dart files. (This was a mechanical commit.)

* Fix weird license headers on Dart files that deviate from our conventions; relicense Shrine.

Some were already marked "The Flutter Authors", not clear why. Their
dates have been normalized. Some were missing the blank line after the
license. Some were randomly different in trivial ways for no apparent
reason (e.g. missing the trailing period).

* Clean up the copyrights in non-Dart files. (Manual edits.)

Also, make sure templates don't have copyrights.

* Fix some more ORGANIZATIONNAMEs

This reverts commit 2b138fd7.

ReorderableListView was constructing a GlobalObjectKey using
the child key as the value. This only had the intended behavior
if the child key was identical across build method invocations.

The new strategy is to scope the child key's value to the
State object's identity, allowing child keys to have value
compare semantics while disambiguating among different list view
instances.

* fix indentof statements in BlockFunctionBody

* fix indentof statements in BlockFunctionBody in tests

* add trailing commas on list/map/parameters

* add trailing commas on Invocation with nb of arg>1

* add commas for widget containing widgets

* add trailing commas if instantiation contains trailing comma

* revert bad change

This converts existing ## Sample code samples to {@tool sample}...{@end-tool} form.

Also:
1. Fixed a minor bug in analyze-sample-code.dart
2. Made the snippet tool only insert descriptions if the description is non-empty.
3. Moved the Card diagram to before the code sample.

* Future<void> main

* Future<void>.delayed

* prefer_void_to_Null

* address review comments

* Improve documentation and clean up code.

* Remove "Note that".

The phrase "note that" is basically meaningless as a prefix to an
otherwise fine sentence.

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests