Break dependency from core/platform/audio to modules/webaudio

This CL breaks the only dependency from core/platform/audio on
modules/webaudio. After this CL, we'll be able to move core/platform/audio into
blink_platform.dll.

R=kbr@chromium.org
BUG=297477

Review URL: https://codereview.chromium.org/25883005

git-svn-id: svn://svn.chromium.org/blink/trunk@159044 bbb929c8-8fbe-4397-9dbb-9b2b20218538
[blink] Rename InCustomSpellcheckDictioanry to InvisibleSpellcheck

This patch renames InCustomSpellcheckDictioanry markers and decorations to
InvisibleSpellcheck. This change hides the intent of the browser in adding
invisible text markers to the text. The resulting markers are more
explicit in their look: they are invisible. The marker purpose should also
be clear: they are for the spellcheck client.

This patch prevents adding multiple invisible marker types. For example,
after this patch we no longer need to add WasMisspelled marker.

This patch is the result of discussion about marker and decoration names
on https://codereview.chromium.org/25740003.

BUG=302807

Review URL: https://codereview.chromium.org/25413004

git-svn-id: svn://svn.chromium.org/blink/trunk@159045 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Disable offsetWidth optimization in perparation for disabling it on M30.

Unfortunately our offsetWidth optimization which made economist.com 2s faster
isn't quite correct.  It caused a bad regression on M30, which was noticed
in the Beta channel.

The code has differed some from the Beta branch, but in an effort to be
as safe as can be, I'm making a very-similar change on Trunk to the
change I'm about to roll into M30.

We will need to fix this optimization and re-enable it once it's safe
in order to get our 2s back on economist.com.

I expect this to slow down some benchmarks.

R=abarth@chromium.org, abarth, enne, tonyg
BUG=290399

Review URL: https://codereview.chromium.org/26355002

git-svn-id: svn://svn.chromium.org/blink/trunk@159046 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Mark fast/forms/placeholder-position.html as flaky

Looks like this has been flaky for a long time.
The failure is in the exact pixel drawing of transform text in a form field.

BUG=304952
R=enne@chromium.org

Review URL: https://codereview.chromium.org/26360002

git-svn-id: svn://svn.chromium.org/blink/trunk@159047 bbb929c8-8fbe-4397-9dbb-9b2b20218538