Revert of Use Opportunity Iterator to position text fragments in NGLineBuilder

Revert of Use Opportunity Iterator to position text fragments in NGLineBuilder (patchset #4 id:80001 of https://codereview.chromium.org/2739683006/ )

Reason for revert:
Test failures on bot:
NGTextLayoutAlgorithmTest.TextFloatsAroundFloatsBefore

https://uberchromegw.corp.google.com/i/chromium.webkit/builders/WebKit%20Android%20%28Nexus4%29/builds/62088

Original issue's description:
> Use Opportunity Iterator to position text fragments in NGLineBuilder
> 
> This patch introduces NGLayoutOpportunityIterator to NGLineBuilder so it
> can use it to search the next available opportunity to position text
> fragments.
> 
> With this patch NGLayout starts supporting a base text floating around
> floats that are positioned before an inline fragment.
> Example:
> <div id="container">
>   <div id="left-float1"></div>
>   <div id="left-float2"></div>
>   <div id="right-float"></div>
>   The quick brown fox jumps over the lazy dog
> </div>
> 
> BUG=635619
> TEST=NGTextLayoutAlgorithmTest::TextFloatsAroundFloatsBefore
> 
> Review-Url: https://codereview.chromium.org/2739683006
> Cr-Commit-Position: refs/heads/master@{#456278}
> Committed: https://chromium.googlesource.com/chromium/src/+/207688fb45319568db61e59c4c8391517793bf47

TBR=kojii@chromium.org,ikilpatrick@chromium.org,glebl@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=635619

[yoichio, 2017-03-13 08:09:08]

The CQ bit was checked by yoichio@chromium.org

[yoichio, 2017-03-13 08:09:09]

Created Revert of Use Opportunity Iterator to position text fragments in
NGLineBuilder

[commit-bot: I haz the power, 2017-03-13 08:09:24]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-03-13 08:11:32]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-03-13 08:11:33]

Try jobs failed on following builders:
  ios-device on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios-device/builds...)
  ios-simulator-xcode-clang on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios-simulator-xco...)