IndexedDB: Histogram available disk space on attempt to open database
https://bugs.webkit.org/show_bug.cgi?id=112862

Reviewed by Adam Barth.

Source/Platform:

* chromium/public/Platform.h:
(WebKit::Platform::availableDiskSpaceInBytes):
(Platform):

Source/WebCore:

ChromeOS suspects they might be hitting disk corruption when the disks
are nearly full. This patch logs the available space to either the
"success" or the "fail" histogram as appropriate so that the
distributions can be compared.

No new tests - I don't know of a good way to test histograms. Local
printf testing didn't turn up any bugs.

* platform/leveldb/LevelDBDatabase.cpp:
(WebCore::HistogramFreeSpace):
(WebCore):
(WebCore::LevelDBDatabase::open):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@146560 268f45cc-cd09-0410-ab3c-d52691b4dbfc