Don't squash into RenderPart subclasses. Don't squash into video elements.

LayoutTests/compositing/squashing/dont-squash-into-videos-expected.txt

Index: LayoutTests/compositing/squashing/dont-squash-into-videos-expected.txt
diff --git a/LayoutTests/compositing/squashing/no-squashing-for-filters-expected.txt b/LayoutTests/compositing/squashing/dont-squash-into-videos-expected.txt
similarity index 60%
copy from LayoutTests/compositing/squashing/no-squashing-for-filters-expected.txt
copy to LayoutTests/compositing/squashing/dont-squash-into-videos-expected.txt
index ecd61c4ee4416b8521c0afce399d26e8d96cb97a..2655f3d2529a178aafef3f81e75b2d9778d71103 100644
--- a/LayoutTests/compositing/squashing/no-squashing-for-filters-expected.txt
+++ b/LayoutTests/compositing/squashing/dont-squash-into-videos-expected.txt
@@ -7,26 +7,26 @@
       "drawsContent": true,
       "children": [
         {
-          "position": [8, 8],
           "bounds": [100, 100],
           "contentsOpaque": true,
           "drawsContent": true,
-          "backgroundColor": "#ADD8E6"
-        },
-        {
+          "backgroundColor": "#ADD8E6",
           "children": [
             {
-              "position": [-5, -5],
-              "bounds": [62, 62],
-              "drawsContent": true,
-              "backgroundColor": "#D3D3D3"
+              "bounds": [100, 100],
+              "drawsContent": true
             },
             {
-              "position": [50, 50],
-              "bounds": [50, 50],
-              "drawsContent": true
+              "bounds": [100, 65]
             }
           ]
+        },
+        {
+          "position": [50, 50],
+          "bounds": [200, 200],
+          "contentsOpaque": true,
+          "drawsContent": true,
+          "backgroundColor": "#D3D3D3"
         }
       ]
     }