By the previous patch, ProgressCenterItemGroup is added to manage the animation
state of progres items and the life time of error items. This CL lets the
ProgressCenterPanel class start to use the class.

The ProgressCenterPanel class has two groups for the normal priority and low
priority. The low priority group is needed for the progress items of drive sync,
which is introduced in the following patch.

BUG=327213
TEST=manually, ProgressCenterItemGroupUnitTest.

Review URL: https://codereview.chromium.org/130933002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244719 0039d316-1c4b-4281-b951-d872f2087c98
When installations are in progress only delay cleaning up of Temp directory, don't delay cleaning up of old extension versions.

This makes the effect of chrome never finishing installing pending extension less severe since most data will still be cleaned up.

BUG=329943

Review URL: https://codereview.chromium.org/131153003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244720 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244720