IndexedDB: Constify some getters, use ContainsKey helper

Review URL: https://codereview.chromium.org/114153004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242032 0039d316-1c4b-4281-b951-d872f2087c98
Do not compile OpaqueBrowserFrameView and co on CrOS

BUG=None
TEST=None
R=oshima
TBR=jamescook

Review URL: https://codereview.chromium.org/115683003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242033 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242032
SVN changes up to revision 242033