Revert of Better handle reentrancy into DocumentLoader::dataReceived().

Revert of Better handle reentrancy into DocumentLoader::dataReceived(). (patchset #10 id:180001 of https://codereview.chromium.org/1263363005/ )

Reason for revert:
ASan bots are reporting a handful of UAFs,

 http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Linux%20ASAN/builds/19837

Original issue's description:
> Better handle reentrancy into DocumentLoader::dataReceived().
> 
> dataReceived() can be called reentrantly if it triggers a nested message
> loop when detaching a Document or parsing script for the new Document.
> Since dataReceived() isn't safe for reentrancy, any nested invocations
> queue the received data to be processed by the top-level invocation of
> dataReceived().
> 
> BUG=515876
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=200436

TBR=japhet@chromium.org,kouhei@chromium.org,morrita@chromium.org,dcheng@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=515876
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=200487

[sof, 2015-08-13 20:03:54]

Created Revert of Better handle reentrancy into DocumentLoader::dataReceived().

[commit-bot: I haz the power, 2015-08-13 20:04:08]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1295553002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1295553002/1

[commit-bot: I haz the power, 2015-08-13 20:04:57]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=200487