Revert of Change fallback font collection in HarfBuzzShaper

Revert of Change fallback font collection in HarfBuzzShaper (patchset #3 id:40001 of https://codereview.chromium.org/1239513004/)

Reason for revert:
Caused a number of tests to crash on Mac 10.6 release that previously only crashed on 10.6 debug. 

media/track/track-cue-rendering-rtl.html
inspector/elements/bidi-dom-tree.html
virtual/antialiasedtext/fast/text/trailing_whitespace_wrapping.html
imported/csswg-test/css-writing-modes-3/text-orientation-script-001k.html
fast/css/word-spacing-characters-complex-text.html
imported/csswg-test/css-writing-modes-3/text-orientation-script-001m.html
virtual/antialiasedtext/fast/text/zero-width-characters-complex-script.html
fast/text/zero-width-characters-complex-script.html
fast/text/trailing_whitespace_wrapping.html

Original issue's description:
> Change fallback font collection in HarfBuzzShaper
> 
> Change HarfBuzzShaper to not populate the fallback font list during text
> shaping and instead populate it based on the ShapeResult objects at call
> time. This circumvents additional registration work and renders the text
> shaping API simpler and more consistent.
> 
> R=leviw@chromium.org
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=198813

TBR=leviw@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=198818

[eae, 2015-07-14 00:45:18]

Created Revert of Change fallback font collection in HarfBuzzShaper

[commit-bot: I haz the power, 2015-07-14 00:45:44]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1239603002/1

[Dirk Pranke, 2015-07-14 00:45:50]

dpranke@chromium.org changed reviewers:
+ dpranke@chromium.org

[Dirk Pranke, 2015-07-14 00:45:50]

lgtm

[commit-bot: I haz the power, 2015-07-14 00:46:57]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=198818