Fix front-end host creation upon navigation

Fix front-end host creation upon navigation

- when navigating, add host bindings to the pending frame rather than old frame;
- force renderer swap if front-end URL is invalid;
- move front-end URL validation to DevToolsUIBindingds

This also re-lands https://codereview.chromium.org/2607833002

BUG=662859, 678035
Review-Url: https://codereview.chromium.org/2620153002
Cr-Commit-Position: refs/heads/master@{#442781}
(cherry picked from commit c2db881506f5709433a5bf6ed981b1bc0c860598)

Review-Url: https://codereview.chromium.org/2653783003 .
Cr-Commit-Position: refs/branch-heads/2924@{#853}
Cr-Branched-From: 3a87aecc31cd1ffe751dd72c04e5a96a1fc8108a-refs/heads/master@{#433059}
Committed: https://chromium.googlesource.com/chromium/src/+/d6f1c251f409263302a2df863df61314418dc4b2

[caseq, 2017-01-24 03:22:50]

Description was changed from

==========
Fix front-end host creation upon navigation

- when navigating, add host bindings to the pending frame rather than old frame;
- force renderer swap if front-end URL is invalid;
- move front-end URL validation to DevToolsUIBindingds

This also re-lands https://codereview.chromium.org/2607833002

BUG=662859,678035

Review-Url: https://codereview.chromium.org/2620153002
Cr-Commit-Position: refs/heads/master@{#442781}
(cherry picked from commit c2db881506f5709433a5bf6ed981b1bc0c860598)
==========

to

==========
Fix front-end host creation upon navigation

- when navigating, add host bindings to the pending frame rather than old frame;
- force renderer swap if front-end URL is invalid;
- move front-end URL validation to DevToolsUIBindingds

This also re-lands https://codereview.chromium.org/2607833002

BUG=662859,678035

Review-Url: https://codereview.chromium.org/2620153002
Cr-Commit-Position: refs/heads/master@{#442781}
(cherry picked from commit c2db881506f5709433a5bf6ed981b1bc0c860598)

Review-Url: https://codereview.chromium.org/2653783003 .
Cr-Commit-Position: refs/branch-heads/2924@{#853}
Cr-Branched-From:
3a87aecc31cd1ffe751dd72c04e5a96a1fc8108a-refs/heads/master@{#433059}
Committed:
https://chromium.googlesource.com/chromium/src/+/d6f1c251f409263302a2df863df6...
==========

[caseq, 2017-01-24 03:22:51]

Committed patchset #1 (id:1) manually as
d6f1c251f409263302a2df863df61314418dc4b2.