PEP8 line length fixes in testing_commands.py

...so that PyLint stops yelling at me
Adds a --component (or -c) argument to test-unit

Example usage:

`./mach test-unit -c style`
Last second bug catch
Corrected case of Document#characterSet

Resolves #4251
Make TextInput correctly handle multibyte chars.
Use .clone() instead of.as_slice().to_string()
auto merge of #4255 : ema-fox/servo/textinput, r=jdm
Implements some HTMLTextAreaElement attributes

These attributes all reflect their own related content values, with the
exception of defaultValue, which acts as an alias for its IDL
textContent attribute.

Many of these do have default values and constraints which are currently unimplemented.
Implements multi line text input for TextArea
Updates WPT to expect newly passing tests

Addresses reviews

More review addressing
HTMLTextArea: Implements a dirty value flag
Handle default uint attributes properly

...and passing a whole bunch of new tests.
Update content tests for Document#characterSet
Make the password input element show the correct number of dots for multibyte chars.
Change time::profile's meta booleans to enums.

This makes these parameters self-documenting.
This patch does not attempt to push those enums into the data
structures that feed calls to this function.

Fixes #4158.
auto merge of #4152 : mttr/servo/textview, r=jdm

Fixes #3918 

Can be tested in `tests/html/textarea.html`. Also implemented some content reflecting IDL attributes for HTMLTextAreaElement while I was in there.

There are some major problems with TextInput when Multiple is enabled that I haven't addressed here, but I'm prepared to open up a follow-up issue.
auto merge of #4256 : ema-fox/servo/password_input, r=jdm
auto merge of #4234 : tterribe/servo/issue4158, r=metajack

This makes these parameters self-documenting.
This patch does not attempt to push those enums into the data
structures that feed calls to this function.

Fixes #4158.
Issue 4253 - Setting timeout on a sync XHR should throw InvalidAccessErr
Split up the InputButton variant