Add a frame sequence number to HistoryItem

Add a frame sequence number to HistoryItem

This will be used by the history system in content/renderer/ to disambiguate
frames during history navigation.

The current system uses two factors to try to find frames for navigation:
frame routing ids, and frame unique names. Routing ids can't be stored for
later use, because they might get saved to disk and collide with routing ids
in a future renderer process. Unique names are more reliable...unless a
website modifies window.name, at which point we try to do lookups based on a
stale name and can't find the right frame.

Instead, we introduce a frame sequence number. Like the existing item and
document sequence numbers, these can be saved to disk with a low chance of
collisions. These can then be reliably used during the current session to
match frames for back/forward navigations.

BUG=393227, 395097
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=178947

[Nate Chapin, 2014-07-24 18:59:31]

darin, would you mind taking a look?

[Nate Chapin, 2014-07-24 19:00:38]

On 2014/07/24 18:59:31, Nate Chapin wrote:
> darin, would you mind taking a look?

https://codereview.chromium.org/412303002/ is the chromium patch to actually use
this.

[darin (slow to review), 2014-07-25 04:39:06]

LGTM

https://codereview.chromium.org/418103003/diff/1/Source/core/loader/HistoryIt...
File Source/core/loader/HistoryItem.h (right):

https://codereview.chromium.org/418103003/diff/1/Source/core/loader/HistoryIt...
Source/core/loader/HistoryItem.h:130: // Used to match frames across
serialization/deserialization more reliably
I think it would be more helpful to add a comment here that defines the new
field, similar to the definitions for the other sequence numbers. What does
frame sequence number represent? How does it evolve, etc.?

[Nate Chapin, 2014-07-25 17:26:34]

The CQ bit was checked by japhet@chromium.org

[commit-bot: I haz the power, 2014-07-25 17:27:34]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/japhet@chromium.org/418103003/20001

[Nate Chapin, 2014-07-25 17:28:18]

The CQ bit was checked by japhet@chromium.org

[commit-bot: I haz the power, 2014-07-25 17:28:20]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/japhet@chromium.org/418103003/20001

[commit-bot: I haz the power, 2014-07-25 18:27:08]

Change committed as 178947