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This patch stores the state of active installs in the InstallTracker
for global access. This allows various install initiators to check for
duplicate installs before proceeding.

Install progress bars in the app launcher can be initialized with the
state of an active install.

BUG=393854
TEST=unit_tests, browser_tests
For manual testing steps, please see bug.

Review URL: https://codereview.chromium.org/389613006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@284014 0039d316-1c4b-4281-b951-d872f2087c98