Revert of FileWriter should not use deprecated {,un}setPendingActivity

Revert of FileWriter should not use deprecated {,un}setPendingActivity (https://codereview.chromium.org/383103002/)

Reason for revert:
Leaks started in:
file-metadata-after-write.html 
file-writer-abort-continue.html 
file-writer-abort-depth.html 
file-writer-abort.html 
file-writer-empty-blob.html 
file-writer-events.html 
file-writer-gc-blob.html 
file-writer-truncate-extend.html 
file-writer-write-overlapped.html 
filesystem-iframe-from-remote.html 
filesystem-url-in-iframe.html 
filesystem-urls-match-self.html 
not-enough-arguments.html 
op-get-metadata.html 
request-file-content.html 
request-metadata.html 
send-file-blob-fail.html 
send-file-blob.html 
shared-worker-constructor.html 

as of:
https://build.chromium.org/p/chromium.webkit/builders/WebKit%20Linux%20Leak/b...

This seems like a likely candidate.


Original issue's description:
> FileWriter should not use deprecated {,un}setPendingActivity
> 
> BUG=354845
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=177936

TBR=nhiroki@chromium.org,tzik@chromium.org,eseidel@chromium.org
NOTRY=true
BUG=354845
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=177988

[kouhei (in TOK), 2014-07-12 01:26:23]

Created Revert of FileWriter should not use deprecated {,un}setPendingActivity

[kouhei (in TOK), 2014-07-12 01:26:43]

The CQ bit was checked by kouhei@chromium.org

[commit-bot: I haz the power, 2014-07-12 01:27:43]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/kouhei@chromium.org/383993008/1

[commit-bot: I haz the power, 2014-07-12 01:28:49]

Change committed as 177988