In LayerTreeCoordinator::adoptImageBackingStore(), there is a PLATFORM(QT) code path to check for identical images, but nothing is done for Cairo, which results in the occurrence of avoidable resource allocations. The issue happens in e.g. http://www.webkit.org/blog-files/leaves/, where there are many leaves flying around while they're produced out of only four bitmaps.
Created attachment 165908 [details]
Comment on attachment 165908 [details]
Clearing flags on attachment: 165908
Committed r129791: <http://trac.webkit.org/changeset/129791>
All reviewed patches have been landed. Closing bug.