Defer setting "internalinstanceid" so that pending (and destroyed)

Defer setting "internalinstanceid" so that pending (and destroyed)
browser plugins can detach before we attach again.

BUG=467614
Test=Load a <webview>
Set its style.display = 'block'.
Observer that it succeeds without <webview> going stale or
throwing any error about "attach" failing.

Committed: https://crrev.com/cbbe20f81b775fb77d545127e6f9771c08a12508
Cr-Commit-Position: refs/heads/master@{#320803}

[lazyboy, 2015-03-16 19:24:04]

lazyboy@chromium.org changed reviewers:
+ fsamuel@chromium.org

[lazyboy, 2015-03-16 19:24:05]

FYI, all WebViewTest.* seems to pass locally, I've sent a trybot run to check
all the tests.

[Fady Samuel, 2015-03-16 20:42:06]

lgtm

[lazyboy, 2015-03-16 22:06:57]

The CQ bit was checked by lazyboy@chromium.org

[commit-bot: I haz the power, 2015-03-16 22:07:50]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1015443002/20001

[commit-bot: I haz the power, 2015-03-16 22:11:39]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-03-16 22:12:54]

Patchset 2 (id:??) landed as
https://crrev.com/cbbe20f81b775fb77d545127e6f9771c08a12508
Cr-Commit-Position: refs/heads/master@{#320803}