Bug 1016558 - Rename some variables to be more meaningful, and update some comments. r=botond r=Cwiiis

Renames:
  displayPortParent -> displayPortAncestor
  scrollParent -> scrollAncestor
  parent -> ancestor
  displayPortParentParent -> displayPortAncestorGrandParent
  layoutDeviceToScrollParentLayer -> layoutDeviceToDisplayPort
  mTransformParentLayerToLayoutDevice -> mTransformDisplayPortToLayoutDevice
  aTransformParentLayerToLayoutDevice -> aTransformDisplayPortToLayoutDevice
Bug 1016558 - Properly account for simple CSS transforms when computing fields for progressive update. r=Cwiiis r=botond
Bug 1016222 - Fuzz a few tests for progressive painting. r=
Bug 1016222 - Ensure async-scroll-1b is run with low-precision painting disabled. r=
Bug 994293 - Enable progressive painting by default on B2G device builds. r=Cwiiis
Bug 897996 - Enable the low-res buffer on B2G. r=Cwiiis
Logging
Bug 1017065 - Prevent the wrong garbage from being drawn and triggering a reftest failure. r=