Generate FrameTree::uniqueName with a URL attribute value.
This CL fixes a bug that navigating back can swap plugin contents.
When a page is loaded by back navigation, we try to load the last
contents into frames. SVG content in <object> is also represented as
a frame internally. The last contents state is stored in a HistoryItem
tree, and HistoryItems for sub-frames are identified by 'uniqueName,'
which depends on frame creation order if frames don't have name
So, if frame creation orders of the first visit and the second visit are
different, we could get incorrect HistoryItem in WebFrameImpl::
How to fix:
This CL tries to generate unique uniqueName even if a frame has no
name attribute. We use an attribute value of Element::
The test was created by email@example.com