Reland of New PaintController under-invalidation checking

third_party/WebKit/LayoutTests/fast/repaint/resources/text-based-repaint.js

 // Asynchronous tests should manually call finishRepaintTest at the appropriate
 // time.
 window.testIsAsync = false;
 window.outputRepaintRects = true;
 
 // All repaint tests are asynchronous.
 if (window.testRunner)
     testRunner.waitUntilDone();
 
 if (window.internals) {
     internals.settings.setUseDefaultImageInterpolationQuality(true);
-    // 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;
+    internals.runtimeFlags.slimmingPaintUnderInvalidationCheckingEnabled = true;
 }
 
 function runRepaintTest()
 {
     if (!window.testRunner || !window.internals) {
         setTimeout(repaintTest, 500);
         return;
     }
 
     if (window.enablePixelTesting)
@@ skipping 47 matching lines @@
     if (window.outputRepaintRects)
         testRunner.setCustomTextOutput(repaintRects);
 
     if (window.afterTest)
         window.afterTest();
 
     // Play nice with async JS tests which want to notifyDone themselves.
     if (!window.jsTestIsAsync)
         testRunner.notifyDone();
 }