Smaller CSSParser UTF16 buffers for escaped strings.

If an ASCII stylesheet contains escaped characters those need to be
unescaped and stored somewhere. The code used to allocate a buffer the
size of the whole CSS file * sizeof(UChar). That meant 700 KB on
arstechnica.com to store a single character. Instead store the
supposedly rare characters in special buffers of appropriate sizes.

BUG=352544

Review URL: https://codereview.chromium.org/196353018

git-svn-id: svn://svn.chromium.org/blink/trunk@170451 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: promote CodeMirror scrollbars to a discrete rendering layer

This patch is a workaround for compositing bug observed on MacBook Pro
with retina display.

BUG=358161

Review URL: https://codereview.chromium.org/219413003

git-svn-id: svn://svn.chromium.org/blink/trunk@170452 bbb929c8-8fbe-4397-9dbb-9b2b20218538