Remove the HashMap in RenderLayerCompositor's overlap map

LayoutTests/compositing/layer-creation/overlap-transformed-layer-with-tranform-body-expected.txt

 (GraphicsLayer

[enne (OOO), 2014/02/28 00:50:13]

typo in test name

[abarth-chromium, 2014/02/28 02:22:08]

:)

   (bounds 800.00 600.00)
   (children 1
     (GraphicsLayer
       (bounds 800.00 600.00)
       (contentsOpaque 1)
+      (drawsContent 1)
       (children 1
         (GraphicsLayer
-          (bounds 800.00 600.00)
+          (position 8.00 8.00)
+          (bounds 784.00 584.00)
           (drawsContent 1)
           (children 2
             (GraphicsLayer
-              (position 8.00 8.00)
-              (bounds 160.00 90.00)
-              (isolate 1)
+              (position 15.00 0.00)
+              (anchor 1.47 0.00)
+              (bounds 256.00 256.00)
               (contentsOpaque 1)
               (drawsContent 1)
-              (backgroundColor #008000)
+              (transform [1.00 0.00 0.00 0.00] [0.00 1.00 0.00 0.00] [0.00 0.00 1.00 0.00] [-10.00 0.00 0.00 1.00])
               (children 1
                 (GraphicsLayer
-                  (bounds 160.00 90.00)
-                  (blendMode multiply)
+                  (position 385.00 0.00)
                 )
               )
             )
             (GraphicsLayer
-              (bounds 800.00 600.00)
-              (drawsContent 1)
+              (bounds 300.00 300.00)
+              (contentsOpaque 1)
             )
           )
         )
       )
     )
   )
 )