<webview>: Fix navigation/attachment race

<webview>: Fix navigation/attachment race

We should not allow attachment after an initial navigation.

Currently, we don't allow attachment after an instance ID is allocated. 

These two checks are not equivalent. We chould have requested an instance ID from
the browser process and then immediately attach a new winow to the <webview> on the next
line prior to getting an instance ID. This will cause attach to get called again.

BUG=244641
Test=manually, this is a race that is extremely hard to test reliably. I will avoid adding
an automated test to avoid introducing more flake.

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=202886

[lazyboy, 2013-05-29 00:38:25]

https://chromiumcodereview.appspot.com/16057004/diff/1/content/renderer/brows...
File content/renderer/browser_plugin/browser_plugin.cc (right):

https://chromiumcodereview.appspot.com/16057004/diff/1/content/renderer/brows...
content/renderer/browser_plugin/browser_plugin.cc:844: // attaching a different
guest.
Can you add a comment: in which case HasNavigated() == true while attachTo is
called? I'm not sure I totally follow.

[Fady Samuel, 2013-05-29 01:28:43]

PTAL

[lazyboy, 2013-05-29 05:22:12]

lgtm

[commit-bot: I haz the power, 2013-05-29 09:47:14]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/fsamuel@chromium.org/16057004/5001

[commit-bot: I haz the power, 2013-05-29 10:17:30]

Step "update" is always a major failure.
Look at the try server FAQ for more details.
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_rel&...

[commit-bot: I haz the power, 2013-05-29 12:02:29]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/fsamuel@chromium.org/16057004/5001

[commit-bot: I haz the power, 2013-05-29 16:48:17]

Change committed as 202886