[SPv2] Introduce an option to output the GraphicsLayer tree as a flat layer list.

third_party/WebKit/LayoutTests/paint/invalidation/resources/text-based-repaint.js

 // Asynchronous tests should manually call finishRepaintTest at the appropriate
 // time.
 window.testIsAsync = false;
 window.outputRepaintRects = true;
+window.outputLayerList = false;
 
 // All repaint tests are asynchronous.
 if (window.testRunner)
     testRunner.waitUntilDone();
 
 if (window.internals) {
     internals.settings.setUseDefaultImageInterpolationQuality(true);
     internals.runtimeFlags.paintUnderInvalidationCheckingEnabled = true;
 }
 
@@ skipping 37 matching lines @@
         return;
 
     // Force a style recalc.
     forceStyleRecalc();
 
     var flags = window.internals.LAYER_TREE_INCLUDES_PAINT_INVALIDATIONS;
 
     if (window.layerTreeAsTextAdditionalFlags)
         flags |= window.layerTreeAsTextAdditionalFlags;
 
+    if (window.outputLayerList)
+        flags |= window.internals.OUTPUT_CHILDREN_AS_LAYER_LIST;
+
     var repaintRects = window.internals.layerTreeAsText(document, flags);
 
     internals.stopTrackingRepaints(document);
 
     // Play nice with JS tests which may want to print out assert results.
     if (window.isJsTest)
         window.outputRepaintRects = false;
 
     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();
 }