Remove a HistoryNode's children when it navigates to a new document.

Remove a HistoryNode's children when it navigates to a new document.

When a reload occurs (or other inert commits), we leave the history tree alone. However, if iframes are dynamically created, we end up with both the old iframes and the new iframes in the history tree, and we never prune them. Instead, if a different-document inert commit occurs, remove the committing node's children, since the corresponding frames are no longer in the frame tree.

BUG=485385
Committed: https://crrev.com/9f3e29c910ce2c2a9c3a60b2675db59d95b8ad3a
Cr-Commit-Position: refs/heads/master@{#329763}

[Nate Chapin, 2015-05-13 23:27:43]

japhet@chromium.org changed reviewers:
+ creis@chromium.org

[Charlie Reis, 2015-05-13 23:35:55]

LGTM

[Nate Chapin, 2015-05-13 23:37:18]

The CQ bit was checked by japhet@chromium.org

[commit-bot: I haz the power, 2015-05-13 23:39:03]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1139033002/1

[commit-bot: I haz the power, 2015-05-14 00:35:26]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-14 00:36:15]

Patchset 1 (id:??) landed as
https://crrev.com/9f3e29c910ce2c2a9c3a60b2675db59d95b8ad3a
Cr-Commit-Position: refs/heads/master@{#329763}

[Charlie Reis, 2015-05-18 21:46:40]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/1148473002/ by creis@chromium.org.

The reason for reverting is: Caused a large spike in crashes across several
bugs:
https://crbug.com/426658
https://crbug.com/488382
https://crbug.com/488421
https://crbug.com/488434
https://crbug.com/488470.