Fix some const-ness and comments

mDrawingState doesn't need to be accessed by the
mStateLock, because by definition it's only accessed
from the main thread.

Similarily, the list of layers in the drawing state
cannot change (ie: is const).

Change-Id: I2e5da7f4d8caee7af7802b432cd45cc81c7c08b0
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index 9566819..0964848 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -304,7 +304,7 @@
                             Vector< sp<LayerBase> >& ditchedLayers);
 
             void        computeVisibleRegions(
-                            LayerVector& currentLayers,
+                            const LayerVector& currentLayers,
                             Region& dirtyRegion,
                             Region& wormholeRegion);
 
@@ -371,7 +371,6 @@
                 // access must be protected by mStateLock
     mutable     Mutex                   mStateLock;
                 State                   mCurrentState;
-                State                   mDrawingState;
     volatile    int32_t                 mTransactionFlags;
     volatile    int32_t                 mTransactionCount;
                 Condition               mTransactionCV;
@@ -395,6 +394,7 @@
                 
                 // Can only accessed from the main thread, these members
                 // don't need synchronization
+                State                       mDrawingState;
                 Region                      mDirtyRegion;
                 Region                      mDirtyRegionRemovedLayer;
                 Region                      mInvalidRegion;