Headless emulator script should use pid argument for logcat

[jdm]

We have code that can determine the pid of the servo app after starting it (see ./mach run --android), so we should use that code to pass a pid argument to logcat and see all of the relevant output for the process.

[highfive]

cc @wafflespeanut

[SimonSapin]

This is the code you mean, right?

servo/python/servo/post_build_commands.py

Lines 97 to 110 in 7c65505

	script = [
	"am force-stop org.mozilla.servo",
	]
	json_params = shell_quote(json.dumps(params))
	extra = "-e servoargs " + json_params
	rust_log = env.get("RUST_LOG", None)
	if rust_log:
	extra += " -e servolog " + rust_log
	script += [
	"am start " + extra + " org.mozilla.servo/org.mozilla.servo.MainActivity",
	"sleep 0.5",
	"echo Servo PID: $(pidof org.mozilla.servo)",
	"exit"
	]

[jdm]

Yep.