Add NavigationEntryImpl::TreeNode for tracking FrameNavigationEntries.

Add NavigationEntryImpl::TreeNode for tracking FrameNavigationEntries.

We still only track the main frame and do not share FNEs across
NavigationEntries, but this new TreeNode class will make it possible
to track them for subtrees and share them across entries of a tab.

BUG=236848
TEST=Existing Navigation{Controller,Entry} tests pass.

Committed: https://crrev.com/5005433dbcebaa2c649f60dea92f05f2ebabf1d0
Cr-Commit-Position: refs/heads/master@{#320730}

[Charlie Reis, 2015-03-12 22:26:16]

Patchset #1 (id:1) has been deleted

[Charlie Reis, 2015-03-12 23:29:54]

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

[Charlie Reis, 2015-03-12 23:29:55]

Next step: Add the tree structure and make FNE refcounted.  This will let us
start filling in the tree and sharing entries in --site-per-process in the next
CL.

https://codereview.chromium.org/1006693002/diff/20001/content/browser/frame_h...
File content/browser/frame_host/frame_navigation_entry.h (left):

https://codereview.chromium.org/1006693002/diff/20001/content/browser/frame_h...
content/browser/frame_host/frame_navigation_entry.h:42: // TODO(creis): Move
virtual URL and related members to FrameNavigationEntry.
Unrelated, but I realized this TODO wasn't true.  I think we only need the
virtual URL for the top-level frame, since it's about what we show in the
address bar.  It can stay on NavigationEntry.

[Charlie Reis, 2015-03-12 23:42:48]

And... I have some tests to debug.  No rush on the review-- I'll let you know
once I track them down.

[Charlie Reis, 2015-03-13 17:58:13]

And, nevermind.  The failures were unrelated and went green with another round
of try jobs. Even the remaining Android failure is flaky and fails for lots of
other folks.

Can you take a look?

[Avi (use Gerrit), 2015-03-13 21:08:03]

lgtm

[Charlie Reis, 2015-03-13 21:26:58]

Great, thanks.  I'll land it on Monday just to be safe, which should give the
previous Clone CL a few days to bake and avoid any unexpected fallout over the
weekend.

[Charlie Reis, 2015-03-16 14:34:17]

The CQ bit was checked by creis@chromium.org

[commit-bot: I haz the power, 2015-03-16 14:34:36]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1006693002/20001

[commit-bot: I haz the power, 2015-03-16 15:52:45]

Committed patchset #1 (id:20001)

[commit-bot: I haz the power, 2015-03-16 15:53:42]

Patchset 1 (id:??) landed as
https://crrev.com/5005433dbcebaa2c649f60dea92f05f2ebabf1d0
Cr-Commit-Position: refs/heads/master@{#320730}