New PaintController under-invalidation checking

third_party/WebKit/LayoutTests/fast/repaint/resources/window-resize-repaint.js

 var testSizes = [
     { width: 600, height: 500 }, // initial size
     { width: 600, height: 250 }, // height decrease
     { width: 400, height: 250 }, // width decrease
     { width: 400, height: 600 }, // height increase
     { width: 800, height: 600 }  // width increase
 ];
 
 var sizeIndex = 0;
 var repaintRects = "";
 
 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 doTest() {
     if (sizeIndex) {
         repaintRects += internals.layerTreeAsText(document, window.internals.LAYER_TREE_INCLUDES_PAINT_INVALIDATIONS);
         internals.stopTrackingRepaints(document);
     }
     ++sizeIndex;
     if (sizeIndex < testSizes.length) {
         internals.startTrackingRepaints(document);
         window.resizeTo(testSizes[sizeIndex].width, testSizes[sizeIndex].height);
         testRunner.layoutAndPaintAsyncThen(doTest);
     } else if (window.testRunner) {
         testRunner.setCustomTextOutput(repaintRects);
         testRunner.notifyDone();
     }
 }
 
 if (window.testRunner) {
     testRunner.useUnfortunateSynchronousResizeMode();
     testRunner.waitUntilDone();
     window.resizeTo(testSizes[0].width, testSizes[0].height);
     testRunner.layoutAndPaintAsyncThen(doTest);
 }