* 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

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

* Allow apps to change the title margin in app bar.

* Fix documentation links and the shouldLayout function in the _ToolbarLayout

* Rename margin to spacing

* review comments

* Test fixes. Now we also test the width to make sure enough space is left for trailing widget

* Expose the middle spacing default and use it in app bar.

* Fix analyzer break

* Doc fixes due to review

* Selectively apply margin between middle and leading

If ToolbarLayout does not have a leading widget, we should not put a margin between leading and middle areas since it ends up being blank space that looks odd. Fixes https://github.com/flutter/flutter/issues/11963

* Fix the failing test which is a good test case for missing leading widget

Fixes #11381

* works using pageview
it’s a bit heavy and scrolls
no documentation or test yet

* docs and tests

* more docs tweak

* revert drive by page view changes

* swap out the indexed stack for a custom thing

* layout everything on the cheap
tests pass

* add more tests

* move back to stack and add docs

* review notes

* build all the tabs once built

Extract layout logic in material app bar to a common file that can be reused for cupertino