Page::backForward() should return a reference.

It is never null.

BUG=none
TEST=none; no behavior changes.

Review URL: https://chromiumcodereview.appspot.com/22873005

git-svn-id: svn://svn.chromium.org/blink/trunk@156365 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: Selection/hover support in both tree and 3d views of Layers panel

BUG=
R=pfeldman@chromium.org

Review URL: https://codereview.chromium.org/22836003

git-svn-id: svn://svn.chromium.org/blink/trunk@156366 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Extract ElementTraversal.h from NodeTraversal.h

TEST=none
BUG=none
R=esprehn,eseidel,jamesr

Review URL: https://chromiumcodereview.appspot.com/22967007

git-svn-id: svn://svn.chromium.org/blink/trunk@156367 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: show owner node selectors in Layers tree

This replaces numeric layer ids with the selectors of their owning nodes.

BUG=
R=pfeldman@chromium.org

Review URL: https://codereview.chromium.org/22888003

git-svn-id: svn://svn.chromium.org/blink/trunk@156368 bbb929c8-8fbe-4397-9dbb-9b2b20218538