Linux sandbox: open /proc with O_CLOEXEC

Prevent one risk of a /proc descriptor leaking by using O_CLOEXEC.

BUG=350145
R=jorgelo@chromium.org

Review URL: https://codereview.chromium.org/189113009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255707 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255707
Add incremental updates for multipage distillation.

Add support for providing incremental updates for multipage
distillation. Updates are now broadcasted to the viewers, whenever a new
page in the article finishes distillation. This allows viewer to show
data to the user, before the distillation of the entire article is
completed.
This change required changing management of pages in distiller to be
refcounted.

BUG=288015
NOTRY=true
R=cjhopman@chromium.org

Review URL: https://codereview.chromium.org/178303004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255708 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255708