Add SessionID::{IdForTab,IdForWindowContainingTab}.

The chain of calls IdForTab is an abbreviation for appears ~17 times, some of
which are their own abbreviations:
http://code.google.com/searchframe#search/&exact_package=chromium&q=%22restore_tab_helper()-%3Esession_id().id()%22

Currently, they're still implemented in terms of the restore_tab_helper, but since tab and window IDs are more fundamental than session restore nowadays, it would be possible to change that if the dependency becomes awkward.

Review URL: https://chromiumcodereview.appspot.com/10680005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@146962 0039d316-1c4b-4281-b951-d872f2087c98
16 files changed