[DevTools] Network Panel: Adjust timing presentation.

1) Fix bar area width to be 200px as expected;
2) Make bars visible even if they are thinner than 1 px;
3) Show duration with hiher precision;
4) Adjust colors (unify hue, saturation and brightness variation);
5) Turn "ssl" to be the same color as enclosing "connecting" bar;
6) Minor refactoring.

See screenshots attached to bug.

BUG=298050

Review URL: https://codereview.chromium.org/23889038

git-svn-id: svn://svn.chromium.org/blink/trunk@158693 bbb929c8-8fbe-4397-9dbb-9b2b20218538