Also, add a few other random dartdocs that I encountered along the way.

There aren't any subclasses of Element that don't also subclass
BuildableElement and I suspect they wouldn't work properly anyway.

Fixes #3656

This change make it easier to track the position of the scroll view without
having to worry about the position object changing out from under the
controller.

The new name follows the pattern of the name suggesting which layout
protocol the parent expects the child to speak.

Fixes #8664

macOS counterpart to c670cd9e.

The new name matches the style guide. (The old name was just old and predated
the style guide.)

Fixes #8000

1. Add `PortScanner` abstraction so that we don't do actual port scanning
   in tests.
2. Don't change the real `cwd` of the isolate during tests, as it affects
   all tests, not just the current running test.

Fixes #8761

gen_snapshot is now used for both JIT and AOT snapshots.  The JIT version
used in debug mode will be a 64-bit binary.

- [x] Add custom logic on MacOS to determine if Java is installed before invoking `java`.
- [x] Check JAVA_HOME, platform specific logic, and finally PATH to locate the `java` executable.
- [x] Improved doctor messages.

Fixes #8508
Fixes #8521

Making the directories read-only causes problems with deletion, which
breaks the Mac chrome buildbot and DeviceLab.

Followup patch to cb2b89c3.

* Use snapshot's .d file as source inputs in Gradle build.

If we don't yet have a .d file (first build), fall back to using the
.dart files in the current directory. This enables us to detect changes
in dependent source files (Flutter framework, packages outside the
source directory, etc.), and re-generate the snapshots as needed.

Unfortunately, Gradle requires knowing the source files before executing
the task, and can't update them after building, so Gradle considers the
second build to be out-of-date (because it has more input files than the
first build). Sub-sequent builds have the correct dependency
information, and will be skipped if the source files haven't changed.

Also added a dependency on gen_snapshot. The snapshot ABI isn't stable,
so we need to re-generate the snapshots when we roll the Dart SDK
dependency.

Fixes #8315
Fixes #8687
Fixes #8607

* update Android part of flutter_view to use the new platform message channel.

* addressed comments

* addressed comments

Changed standard encoding to use host endianness. Engine roll.

This patch covers multi-box adaptor and the viewports.

Provides a strong hint to developers that editing Flutter framework
headers isn't supported.

It was resulting in weird situations where the tool would dump an
error message and stack but not quit, or would fail hard but then just
hang.

Instead, specifically catch errors you expect. As an example of this,
there's one error we expect from the DartDependencySetBuilder, so we
catch that one, turn it into a dedicated exception class, then in the
caller catch that specific exception.

Most of these docs were already in place, but this patch adds the remaining
missing ones.

Fixes #8618

Also, some renames for more accuracy.

* do not forward status if stream is closed
* remove devfs test timeout

Add the minimum set of required properties for run_recipe.py and where
to look them up.

These symbols were not intended to be public. Also, remove some bogus dartdocs
for PhysicalModeLayer.

(follow-on to #8698)

Windows' built-in unzippers are painfully slow. It drives me mad!

Unzip SDK with 7-Zip: ~10s
Unzip SDK with Windows: ~90s

Changing to an inline function, making the type more clear.

* Rename `Device.platform` to `Device.targetPlatform` to avoid
  collision with the exported variable from `platform.dart`

`all.dart` is no longer needed. Furthermore, it causes tests to
be skipped, or to silently fail to run anything.

Fixes #7941