Set the minimum timer interval on a per-page basis, and adjust it when
tabs are brought to the foreground and sent to the background.

This CL does not actually increase the background timer interval. That
will be done separately, so that it can easily be reverted without
removing all of the associated code.

BUG=66078
TEST=none (tested manually with minimal test case)

Review URL: http://codereview.chromium.org/6532012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@75404 0039d316-1c4b-4281-b951-d872f2087c98
7 files changed