Merge 94892 - Pepper quota support

Merge 94892 - Pepper quota support

Probably this could be better implemented using push notification model, but in this patch I made this very straightforwardly (with possibly minimal change).

* Added QuotaFileIO class (in quota_file_io.{cc,h}) which performs pre- and post- write quota related operations.
* For Write/SetLength the QuotaFileIO instance first performs QueryFileInfo and QueryAvailableSpace to get the file size and current available space.  If the results look good it dispatches actual Write/SetLength operations.  After the operation has succeeded it then notifies the browser that it has made a storage modify operation.
* For WillWrite/WillSetLength this change assumes they are always followed by actual write/setlength operations and the operations will succeed.

Based on another cleanup patch:
http://codereview.chromium.org/7438001/

BUG=86556
TEST=QuotaFileIOTest.*

Review URL: http://codereview.chromium.org/7433006

TBR=kinuko@chromium.org
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=96769