New PaintController under-invalidation checking

third_party/WebKit/LayoutTests/resources/run-after-layout-and-paint.js

 // Run a callback after layout and paint of all pending document changes.
 //
 // It has two modes:
 // - traditional mode, for existing tests, and tests needing customized notifyDone timing:
 //   Usage:
 //     if (window.testRunner)
 //       testRunner.waitUntilDone();
 //     runAfterLayoutAndPaint(function() {
 //       ... // some code which modifies style/layout
 //       if (window.testRunner)
 //         testRunner.notifyDone();
 //       // Or to ensure the next paint is executed before the test finishes:
 //       // if (window.testRunner)
 //       //   runAfterAfterLayoutAndPaint(function() { testRunner.notifyDone() });
 //       // Or notifyDone any time later if needed.
 //     });
 //
 // - autoNotifyDone mode, for new tests which just need to change style/layout and finish:
 //   Usage:
 //     runAfterLayoutAndPaint(function() {
 //       ... // some code which modifies style/layout
 //     }, true);
 
-if (window.internals) {
-    // TODO(wangxianzhu): Some spv2 tests crash with under-invalidation-checking
-    // because the extra display items between Subsequence/EndSubsequence for
-    // under-invalidation checking breaks paint chunks. Should fix this when fixing
-    // crbug.com/596983.
-    if (!internals.runtimeFlags.slimmingPaintV2Enabled)
-        internals.runtimeFlags.slimmingPaintUnderInvalidationCheckingEnabled = true;
-}
+if (window.internals)
+    internals.runtimeFlags.slimmingPaintUnderInvalidationCheckingEnabled = true;
 
 function runAfterLayoutAndPaint(callback, autoNotifyDone) {
     if (!window.testRunner) {
         // For manual test. Delay 500ms to allow us to see the visual change
         // caused by the callback.
         setTimeout(callback, 500);
         return;
     }
 
     if (autoNotifyDone)
         testRunner.waitUntilDone();
 
     testRunner.layoutAndPaintAsyncThen(function() {
         callback();
         if (autoNotifyDone)
             testRunner.notifyDone();
     });
 }