Avoid collapsing anonymous block children already being destroyed

When normalizing a block with anonymous blocks for first-letter,
before content, and contained text, a collapsing anonymous block
cascade is triggered that attempts to collapse the contained
text's anonymous block within its destruction method. To avoid
this, adding logic to bail early if we're already destroying
the child anonymous block we're trying to collapse.

While in the function, doing a little cleanup to make it more
obvious that it only operates on RenderBlocks, not RenderBoxes,
and updating some of the comments to hopefully be more useful.

BUG=282088

Review URL: https://chromiumcodereview.appspot.com/23463021

git-svn-id: svn://svn.chromium.org/blink/trunk@157392 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Set initial vector capacity to 4, down from 16.

Measurements notes in the bug note that this is a reasonable
memory saving. Perf seems unimpacted by the smaller default.

BUG=285442
R=abarth@chromium.org

Review URL: https://codereview.chromium.org/23453040

git-svn-id: svn://svn.chromium.org/blink/trunk@157393 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add myself to Source/web OWNERS.

I intend to review changes related to input events, scrolling/scaling,
viewport meta tag, fixed layout size, and Android-specific features
(I'll delegate review of other areas to other OWNERS).

NOTRY=true
BUG=

Review URL: https://chromiumcodereview.appspot.com/23731009

git-svn-id: svn://svn.chromium.org/blink/trunk@157394 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add UseCounter for SVGAnimateColorElement

This patch adds a use counter for animateColor.

BUG=286197

Review URL: https://chromiumcodereview.appspot.com/23857007

git-svn-id: svn://svn.chromium.org/blink/trunk@157395 bbb929c8-8fbe-4397-9dbb-9b2b20218538