Fix a crasher

TBR=alecflett
BUG=262998

Review URL: https://codereview.chromium.org/24907002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226069 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226069
ActivityLogDatabasePolicy calls a virtual method from its
constructor which causes occasional test crashes on Windows
and Linux.

This fix adds Init method to ActivityLogDatabasePolicy class
which further initializes the object after the constructor.
Now, the virtual method is called from the Init method.

BUG=300013

Review URL: https://codereview.chromium.org/25040005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226070 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226070