Provide some debug-mode time hooks to visually debug painting and layout.

Provide some debug-mode time hooks to visually debug painting and layout.

There's four hooks: one draws a teal box around the size, one draws a
green line and an orange line at the alphabetic and ideographic
baselines, and one clips at the paintBounds.

I also implemented Rect.shift() and Rect.inflate() to adjust Rects in
various ways that were helpful while developing this.

The baseline logic now lets you ask for the baseline _without_ the
no-baseline adjustment, in case you only care about the baseline when
there is a real one.

R=abarth@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/c5050c7b1d1648dc6f6e97b4a7ab463c85b67b20

[abarth-chromium, 2015-07-14 17:18:31]

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

[abarth-chromium, 2015-07-14 17:18:31]

lgtm

[Hixie, 2015-07-14 17:19:33]

Committed patchset #3 (id:40001) manually as
c5050c7b1d1648dc6f6e97b4a7ab463c85b67b20 (presubmit successful).