[SurfaceFlinger] Update comments to clarify transform.

Clarify the source coordinate space and destination coordinate space for
transforms.

Bug: N/A
Test: N/A
Change-Id: I93f6770f8a1f03f81e30e42a80c3196ccb1b0fee
diff --git a/services/surfaceflinger/Layer.h b/services/surfaceflinger/Layer.h
index 02593d5..ad8ee32 100644
--- a/services/surfaceflinger/Layer.h
+++ b/services/surfaceflinger/Layer.h
@@ -1076,7 +1076,8 @@
     sp<Layer> getRootLayer();
 
     // Cached properties computed from drawing state
-    // Effective transform taking into account parent transforms and any parent scaling.
+    // Effective transform taking into account parent transforms and any parent scaling, which is
+    // a transform from the current layer coordinate space to display(screen) coordinate space.
     ui::Transform mEffectiveTransform;
 
     // Bounds of the layer before any transformation is applied and before it has been cropped