Switch from CommandLine switch to WebPreferences to control Pepper 3D.

This is to get us ready to dynamically enable or disable a renderer feature whenever, for example, the gpu is switched in a multiple gpu system.

BUG=332188
TEST=
R=bbudge@chromium.org, jamesr@chromium.org, joi@chromium.org, kbr@chromium.org

Review URL: https://codereview.chromium.org/126993002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244212 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244212