Invalidate objects when containing block changed

third_party/WebKit/LayoutTests/fast/repaint/stacking-context-lost-expected.txt

 {
   "bounds": [800, 600],
   "children": [
     {
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
-      "repaintRects": [

[chrishtr, 2015/10/30 18:28:18]

Why would this CL lead to less invalidation?

[Xianzhu, 2015/10/30 19:15:28]

Previously spurious invalidation occurs in the following case:
1. the object is invalidated on the previous paint invalidation container;
2. the object is moved to the new paint invalidation container;
3. the object is removed or changed.

The invalidation is issued at step 3 for the object's
previousPaintInvalidationRect on the original paint invalidation container which
is incorrect. Now we clear it when previous paint invalidation rect is
invalidated on the original paint invalidation container, and there will be no
invalidation for previousPaintInvalidation after paint invalidation container
changes.

[Xianzhu, 2015/10/30 19:44:40]

Rereading found this sentence is not clear:

"The invalidation is issued at step 3 for the object's
previousPaintInvalidationRect on the original paint invalidation container which
is incorrect."

Explanation: The previousPaintInvalidationRect was calculated on the original
paint invalidation container, so it's incorrect to invalidate it on the new
paint invalidation container.

-        [0, 0, 100, 100]
-      ],
       "paintInvalidationClients": [
         "LayoutBlockFlow (relative positioned) DIV id='inner'"
       ],
       "children": [
         {
           "position": [278, 278],
           "bounds": [100, 100],
           "contentsOpaque": true,
           "drawsContent": true,
           "backfaceVisibility": "hidden",
           "backgroundColor": "#008000",
           "repaintRects": [
             [0, 0, 100, 100],
             [0, 0, 100, 100],
             [0, 0, 100, 100]
           ],
           "paintInvalidationClients": [
             "LayoutBlockFlow (relative positioned) DIV id='outer'",
             "LayoutBlockFlow (relative positioned) DIV id='inner'",
             "LayoutBlockFlow (relative positioned) DIV id='outer'"
           ]
         }
       ]
     }
   ]
 }