Merge 157392 "Avoid collapsing anonymous block children already ..."

Merge 157392 "Avoid collapsing anonymous block children already ..."

> 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

TBR=leviw@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=157549

[leviw_travelin_and_unemployed, 2013-09-10 21:06:48]

Committed patchset #1 manually as r157549.