Fix HTML5 video streaming.

Fix HTML5 video streaming.

AsyncResourceHandler was clearing the back-pointer stored on the
request info prematurely.  This caused us to miss many of the
DataReceived_ACK messages.  As a result, we'd get into a state
where we'd never resume downloading.

BUG=133808
R=jam@chromium.org
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=143341

[darin (slow to review), 2012-06-20 23:02:27]

I'm working on a proper unit test for this, but since this CL fixes a pretty
major regression, I'm sending this out without a test first :(

[darin (slow to review), 2012-06-20 23:03:42]

https://chromiumcodereview.appspot.com/10599002/diff/5/content/browser/render...
File content/browser/renderer_host/buffered_resource_handler.cc (left):

https://chromiumcodereview.appspot.com/10599002/diff/5/content/browser/render...
content/browser/renderer_host/buffered_resource_handler.cc:397: next_handler_ =
handler.Pass();
NOTE:  The old ResourceHandler gets destroyed here.  That causes
~CrossSiteResourceHandler and ~AsyncResourceHandler to run, which has the effect
of calling set_{cross_site,async}_handler(NULL).

[jam, 2012-06-20 23:16:49]

lgtm

[commit-bot: I haz the power, 2012-06-20 23:41:28]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/darin@chromium.org/10599002/5