GitLab

Perform NaCl initialization during app_shell's startup path similar to
how Chrome initializes it.
* Refactor some of the lazy background page impulse code into ProcessManager so it can be shared with Chrome

BUG=400577
TEST=manual tests of app_shell, existing ProcessManager unit tests and browser tests

Review URL: https://codereview.chromium.org/437503004

Cr-Commit-Position: refs/heads/master@{#290082}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@290082 0039d316-1c4b-4281-b951-d872f2087c98