Terminal: Add support for (and "fix") backspace.

Terminal: Add support for (and "fix") backspace.

Also:
* Fix consecutive spaces (don't collapse them).
* Add support for ^L.

Still doesn't work:
* Totally blank lines. (I know why, but I don't know why I can't seem to
  fix it.)

R=erg@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/8b754a508f50c6b4604ccce95c7b0d3fe960f35b

[Elliot Glaysher, 2015-03-11 23:33:49]

lgtm

https://codereview.chromium.org/997873004/diff/1/sky/examples/terminal/termin...
File sky/examples/terminal/terminal.sky (right):

https://codereview.chromium.org/997873004/diff/1/sky/examples/terminal/termin...
sky/examples/terminal/terminal.sky:97: _control.lastChild.textContent =
oldText.substring(0, oldText.length - 1);
Looking forward to your implementation of 'ESC[K'!

[viettrungluu, 2015-03-11 23:54:21]

Committed patchset #2 (id:20001) manually as
8b754a508f50c6b4604ccce95c7b0d3fe960f35b (presubmit successful).

[ojan, 2015-03-12 20:11:47]

ojan@chromium.org changed reviewers:
+ ojan@chromium.org

[ojan, 2015-03-12 20:11:48]

https://codereview.chromium.org/997873004/diff/20001/sky/examples/terminal/te...
File sky/examples/terminal/terminal.sky (right):

https://codereview.chromium.org/997873004/diff/20001/sky/examples/terminal/te...
sky/examples/terminal/terminal.sky:66: void _handleKeyDown(KeyboardEvent event)
{
FWIW, you're better off just not using keypress. Use keydown for everything. We
need to remove keypress from the platform.

As for the contentedtiable thing, it appears we've broken tabindex (the standard
way of making something focusable on the web.