…st integration_test`" (#170686)"

This reverts commit b5dbfc3.

…est integration_test`" (#170686)" (#170718)

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Reverts: #170686
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Initiated by: matanlurey
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Reason for reverting: Broke [`Windows_mokey
native_assets_android`](https://ci.chromium.org/ui/p/flutter/builders/prod/Windows_mokey%20native_assets_android/2518/overview)
again.
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Original PR Author: dcharkes
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Reviewed By: {bkonyi, matanlurey}
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This change reverts the following previous change:
Reland #170374

Original PR in first commit. Fixes in subsequent commits:

* `flutter` is not on the `PATH` in the device lab, use `_flutterBin`
(consistent with the rest of the test).
   Fixes `flutter` not found.
* `flutter test integration_test` now does not build assets for the host
anymore. `flutter test` builds assets for the host. The `TestCommand` is
now special-case to check for `_isIntegrationTest`.
Fixes `clang++` not found. (It's the compiler for Linux, but we are
running integration tests on an Android device.)

Tests pass locally with:

```
$ cd /Users/dacoharkes/src/flutter/flutter/dev/devicelab && dart bin/test_runner.dart test -t native_assets_android
```

Note:

* The device lab tests are not run on presubmit until
#170682 is addressed.
* The emulator tests are not run at all atm:
#170529.
<!-- end_revert_body -->

Co-authored-by: auto-submit[bot] <[email protected]>

…ration_test`" (#170728)

Reland #170686.

Closes: #168961.

Original PR in first commit. Fix in subsequent commit:

* Do process invocation of `flutter pub add` in a different way.
   Fixes: `ProcessException: %1 is not a valid Win32 application`

Reproduced locally by changing
dev/devicelab/bin/tasks/native_assets_android.dart to
`DeviceOperatingSystem.windows` and verified the `flutter pub add` call
now succeeds.

(Also, moved the add integration test into the create test project to
avoid having multiple `flutter pub get`s.)

Third time is the charm.

…test integration_test`" (flutter/flutter#170686)

…test integration_test`" (flutter/flutter#170686)

…test integration_test`" (flutter/flutter#170686)

…test integration_test`" (flutter/flutter#170686)

…test integration_test`" (flutter/flutter#170686)

…test integration_test`" (flutter/flutter#170686)

…test integration_test`" (flutter/flutter#170686)

…test integration_test`" (flutter/flutter#170686)

…test integration_test`" (flutter/flutter#170686)

…test integration_test`" (flutter/flutter#170686)

…test integration_test`" (flutter/flutter#170686)

…test integration_test`" (flutter/flutter#170686)

…test integration_test`" (flutter/flutter#170686)

…test integration_test`" (flutter/flutter#170686)

…test integration_test`" (flutter/flutter#170686)

…test integration_test`" (flutter/flutter#170686)

…test integration_test`" (flutter/flutter#170686)