Fix flutter run --use-application-binary

[johnmccutchan]

When using --use-application-binary:

• Stop flutter run from checking for a pubspec.yaml in current directory
• Stop flutter run from invoking pub get
• Set 'shouldBuild' based on --use-application-binary
• Stop requiring 'lib/main.dart' to be present before running.
• Stop building an FLX when launching on Android

Generally, the code for 'running' an application on a device is conflated with 'building' a snapshot/bundle/OS-specific package, I started pulling on this thread but then backed off because the problem is so pervasive. This is sufficient for developers to start using:

$ flutter run --use-application-binary ~/path/to/built.apk

@tvolkert @devoncarew

[tvolkert]

LGTM

[devoncarew]

lgtm

The checks for a pubspec.yaml file should turn off when passing in an explicit .packages file path (--packages=...): https://github.com/flutter/flutter/blob/master/packages/flutter_tools/lib/src/runner/flutter_command.dart#L210. I assume a --packages arg will be necessary when running via --use-application-binary? Or perhaps just necessary when running in hot mode.

[Hixie]

What's the purpose of this command? What is Flutter-specific about it?

[johnmccutchan]

@devoncarew --packages is not necessary for non-hot mode as we already have a fully built apk including script snapshot.