Bug 877300 - Add a basic DOM walker actor. r=jwalker

--HG--
extra : rebase_source : 984ca53aba9223f1d7c716a394cef2fc72bf8438
Bug 878379 - Change the walker's querySelector requests to provide any nodes needed to connect to the root node. r=jwalker

--HG--
extra : rebase_source : c234f32af28b5c137e679b1da1d9e5967fc08b3f
Bug 878381 - Keep track of parents and children on the client side of the inspector. r=jwalker

--HG--
extra : rebase_source : c8ba58bf283e6c2c99c0c1ba8959ce97fc266d8a
Bug 878441 - Add simple mutation watching to the inspector actor. r=jwalker

--HG--
extra : rebase_source : 1f6a187ccaa8a8d0454da7271a5adbfd890c7c79
Bug 878442 - Add tree change mutations to the inspector actor. r=jwalker

--HG--
extra : rebase_source : 54401ddc820a0636f2980b8051207c4fa9968113
Bug 878614 - Handle subdocument loads/unloads in the inspector actor. r=jwalker

--HG--
extra : rebase_source : 08d33498922f3a8b46faa5b1b11c6d8d25de9f17
Bug 878443 - Let the inspector actor expire actors for nodes that are no longer connected to the tree. r=jwalker

--HG--
extra : rebase_source : 0f6e871eebfd817b70d8229127b6cd285950ea86