hooked up XmlPrettyPrinter with ManifestMerger

Fixed a bug I introduced in XmlPositionParser by now flushing any
pending TEXT node when encountering a COMMENT node.

Added tests to ensure pretty printer is invoked when serializing
an xml document.

Change-Id: Ib17856b7dddd6ff8a6515b153d8aa4433fe5d7b6
Merge "hooked up XmlPrettyPrinter with ManifestMerger" into idea133
Added ability to save and reload manifest merger actions.

Split ActionRecorder which is not used to record actions during the
merging activities and Actions which is the resulting object once
merging is finished. Actions can be pesisted to an xml document
and reloaded from one.

Started provided some convenience APIs on Actions to retrieve actions
per element or attribute.

Implemented a simple ResultMapping to be able to get a pointer for
each resulting merged xml line to the original location that line
came from.

Change-Id: I8f073d34471928151cf1f12a84137390feb377ae
Merge "Added ability to save and reload manifest merger actions." into idea133
Merge remote-tracking branch 'aosp/idea131' into instrumentation_runner_options