Verify that reftest passes valid servo args

Fixes #4101
infer_test_by_dir cleanup

No actual change in functionality here. I was just unhappy with the way
test-ref was singled out before, and realized an obvious fix.
Fixed test filter
auto merge of #4168 : mttr/servo/mach_inferred_test_cleanup, r=Manishearth

No actual change in functionality here. I was just unhappy with the way test-ref was singled out before, and realized an obvious fix.
Fix error in layout trace viewer
auto merge of #4155 : mttr/servo/reftest_unknown_servo_args, r=jdm

Fixes #4101
auto merge of #4169 : IdeaHat/servo/fix-mach-unit-test-filter, r=jdm

Minor change, added unit test filter to components so that ./mach test-unit [test-filter] works in line with documentation.

I'd personally like to also make filters on the components as well as the tests. This would change the interface (probably to ./mach test-unit [component-filter] [test-filter]), but change is NOT in this pull request.
auto merge of #4186 : mbrubeck/servo/layout-viewer, r=glennw

d1b433a3b3bab353f320b2f39fa953ce326d2d55 changed the encoding format for Flows.  The root is no longer wrapped inside a `data` field, but instead includes BaseFlow fields directly.  This broke the layout trace viewer, which threw an uncaught exception when the `data` property was missing.  This fixes the exception, though some functionality may still be partly broken.
Move the servo crate from root to components/servo
Warn when Cargo is run directly. Fix #3957.
Make build system more independent of current directory.
Have `./mach cargo` not change to `components/servo`.

`ports/android/glut` relies on it executing on the current directory.
Fix up android/glut port to find its servo dependency.
Don’t try to run unit tests for the servo crate.

There are none, but the contenttest program fails with:

```
task '<main>' panicked at 'Required option 'source-dir' missing.', ../../tests/contenttest.rs:48
```
More target path fixup.
auto merge of #4140 : SimonSapin/servo/no-root-cargo-toml, r=SimonSapin

This fixes #3957, and allow #4115 not to regress #4099.
ports/cef: Implement accelerated compositing for the CEF port.