Revert "[DevTools] Refactor docking code." Caused browser_tests failures in DevToolsSanityTest.TestDevToolsExternalNavigation.

This reverts commit 1ae43fefb40a837956152f246f10a3a313055d63 (r164292).

BUG=318751
TBR=dgozman

Review URL: https://codereview.chromium.org/119353004

git-svn-id: svn://svn.chromium.org/blink/trunk@164297 bbb929c8-8fbe-4397-9dbb-9b2b20218538