Remove transitional WEBLAYER_IS_PURE_VIRTUAL code

The code guarded by !defined(WEBLAYER_IS_PURE_VIRTUAL) is dead as of
http://trac.webkit.org/changeset/126076. Also removes WEBCONTENTLAYERCLIENT_FLOAT_OPAQUE_RECT
code, which has been dead since WebKit r108829

BUG=


Review URL: https://chromiumcodereview.appspot.com/10831396

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@153132 0039d316-1c4b-4281-b951-d872f2087c98
5 files changed