Don't clip invalidation of composited scrolling contents

LayoutTests/compositing/repaint/should-not-clip-composited-scrolling-layer2-expected.txt

 {
   "bounds": [800, 600],
   "children": [
     {
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "children": [
         {
           "position": [8, 8],
-          "bounds": [200, 200],
+          "bounds": [500, 500],
           "drawsContent": true,
           "repaintRects": [
-            [0, 0, 185, 200]
+            [0, 0, 500, 500],
+            [0, 0, 500, 500]

[Xianzhu, 2014/09/10 23:45:13]

This is not fully correct that both the container and and contents layer are
invalidated. Will fix it later.

           ],
           "children": [
             {
-              "bounds": [185, 185],
+              "bounds": [485, 485],
               "children": [
                 {
-                  "bounds": [185, 1200],
+                  "bounds": [5000, 5000],
                   "shouldFlattenTransform": false,
                   "drawsContent": true,
                   "repaintRects": [
-                    [0, 0, 185, 200]
+                    [2000, 2000, 3000, 3000],

[Xianzhu, 2014/09/10 23:45:13]

This is because of the previousPaintInvalidationRect. Will fix it later.

+                    [0, 0, 5000, 5000]
                   ],
                   "children": [
                     {
                       "shouldFlattenTransform": false
                     }
                   ]
                 }
               ]
             },
             {
               "children": [
                 {
-                  "position": [0, 185],
-                  "bounds": [185, 15],
-                  "drawsContent": true
-                },
-                {
-                  "position": [185, 0],
-                  "bounds": [15, 185],
+                  "position": [0, 485],
+                  "bounds": [485, 15],
                   "drawsContent": true,
                   "repaintRects": [
-                    [0, 0, 15, 185],
-                    [0, 0, 15, 185],
-                    [0, 0, 15, 185]
+                    [0, 0, 485, 15]
                   ]
                 },
                 {
-                  "position": [185, 185],
+                  "position": [485, 0],
+                  "bounds": [15, 485],
+                  "drawsContent": true,
+                  "repaintRects": [
+                    [0, 0, 15, 485]
+                  ]
+                },
+                {
+                  "position": [485, 485],
                   "bounds": [15, 15],
                   "drawsContent": true
                 }
               ]
             }
           ]
         }
       ]
     }
   ]
 }