Move wm/core to wm namespace.

Also sets up new targets for wm_core, wm_core_unittests, etc.

R=sky@chromium.org
TBR=sky@chromium.org
BUG=

Review URL: https://codereview.chromium.org/196063002

git-svn-id: http://src.chromium.org/chrome/trunk/src/testing@256680 4ff67af0-8c30-449e-8e8b-ad334ec8d88c
Revert "Move wm/core to wm namespace."

This reverts commit 067d7fe616a07011b9e2d2609fc65af8db6a7dfb.

Broke the build:
http://build.chromium.org/p/chromium.mac/builders/Mac%20Builder%20%28dbg%29/builds/63598/steps/compile/logs/stdio

BUG=
TBR=ben

Review URL: https://codereview.chromium.org/198283002

git-svn-id: http://src.chromium.org/chrome/trunk/src/testing@256686 4ff67af0-8c30-449e-8e8b-ad334ec8d88c