Fire "dreaming started" and "dreaming stopped" broadcasts.

Dream manager now fires broadcast intents when entering + exiting
dreamland (except when testing).

Power manager can now listen for dreams ending, using polling only
as a backstop.

Also:
 - Bullet-proof dream-manager/dream against known failure modes
 - Add new read/write dream permissions
 - Refactor dream-manager to delegate work + state management into
   a new DreamController class, via a handler

Bug:6999949
Bug:7152024
Change-Id: I986bb7812209d8c95ae1d660a5eee5998a7b08b1

Author: John Spurlock

api/current.txt

@@ -20289,6 +20289,8 @@ package android.service.dreams {
     method public void setContentView(android.view.View);
     method public void setContentView(android.view.View, android.view.ViewGroup.LayoutParams);
     method public void setInteractive(boolean);
+    field public static final java.lang.String ACTION_DREAMING_STARTED = "android.intent.action.DREAMING_STARTED";
+    field public static final java.lang.String ACTION_DREAMING_STOPPED = "android.intent.action.DREAMING_STOPPED";
     field public static final java.lang.String METADATA_NAME_CONFIG_ACTIVITY = "android.service.dreams.config_activity";
     field public static final java.lang.String SERVICE_INTERFACE = "android.service.dreams.Dream";
   }