Use bit fields inside cc to reduce memory usage.

Using bitfields we get the memory usage as follows

+-----+---------------------------+------------------------+---------+
|.No..|.Class/Structure/File......|.Size.of.object.(bytes).|.Memory..|
|.....|...........................+------------------------+.Reduced.|
|.....|...........................|...Before..|...After....|.........|
+-----+---------------------------+-----------+------------+---------+
|..1..|.cc::Layer.................|......840..|.....824....|......16.|
+-----+---------------------------+-----------+------------+---------+
|..2..|.cc::LayerImpl.............|......880..|.....864....|......16.|
+-----+---------------------------+-----------+------------+---------+
|..3..|.cc::RenderSurfaceImpl.....|......408..|.....400....|.......8.|
+-----+---------------------------+-----------+------------+---------+

Review URL: https://codereview.chromium.org/102733006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239682 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239682
Move out DidStartProvisionalLoad from WebContentsImpl into Navigator.

BUG=304341

Review URL: https://codereview.chromium.org/26316005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239683 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239683