Update javadocs for DreamService.
Update javadocs for DreamService.

Reflect the new intent-filter protocol, and add a bit about <dream>.
Also escape xml so it's visible in generated html.

Bug:7256474
Change-Id: Id270eeb70601b492458834f19216801b428af4cb

xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base