PlzNavigate: Properly call WebContents::DidStartNavigatingToPendingEntry

PlzNavigate: Properly call WebContents::DidStartNavigatingToPendingEntry

This CL makes it so that NavigatorImpl::Navigate will call
DidStartNavigatingToPendingEntry after creating the NaviagtionRequest when
PlzNavigate is enabled. This makes the test
NavigationControllerTest.ReloadOriginalRequestURL pass with PlzNavigate
enabled.

BUG=439423
Committed: https://crrev.com/22fa94fe6be395c363d222b1262c9e8239c6aabc
Cr-Commit-Position: refs/heads/master@{#322543}

[clamy, 2015-03-26 15:16:51]

clamy@chromium.org changed reviewers:
+ carlosk@chromium.org, fdegans@chromium.org, nasko@chromium.org

[clamy, 2015-03-26 15:17:30]

@nasko, carlosk: PTAL
@fdegans: FYI

This fixes the test NavigationControllerTest.ReloadOriginalRequestURL.

[nasko, 2015-03-26 20:32:09]

LGTM

[carlosk, 2015-03-27 09:38:43]

LGTM

[clamy, 2015-03-27 10:23:27]

The CQ bit was checked by clamy@chromium.org

[commit-bot: I haz the power, 2015-03-27 10:23:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1035953002/1

[commit-bot: I haz the power, 2015-03-27 10:27:16]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-27 10:28:19]

Patchset 1 (id:??) landed as
https://crrev.com/22fa94fe6be395c363d222b1262c9e8239c6aabc
Cr-Commit-Position: refs/heads/master@{#322543}