Move navigation and frame tree classes to a new frame_host/ directory.

This CL moves all frame tree classes, Navigation* and its dependencies from web_contents/ to a separate frame_host/ directory.

BUG=304341

Review URL: https://codereview.chromium.org/49823002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@231921 0039d316-1c4b-4281-b951-d872f2087c98
Do not discard the first run when some cold runs are requested.

When cold runs are requested, it is not necessary to systematically discard the
first run, as this is another cold run.

Review URL: https://codereview.chromium.org/52473002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@231922 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 231921
SVN changes up to revision 231922