Fix Compositing of Opaque Scrolling Layers and Add Tests

third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp

Index: third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp b/third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp
index 8ae2819e6a25525fb5c6aeba17bda724df869e7d..45fb553060e862cda2b80123bb61e2ba2348e329 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp
@@ -238,16 +238,10 @@ void CompositingRequirementsUpdater::updateRecursive(PaintLayer* ancestorLayer,
 
         if (reasonsToComposite && layer->scrollsOverflow() && !layer->needsCompositedScrolling()) {
             // We will only set needsCompositedScrolling if we don't care about
-            // the LCD text hit, we may be able to switch to the compositor
+            // the LCD text hit, or when the background supports painting LCD text.
+            // We may be able to switch to the compositor
             // driven path if we're alread composited for other reasons and are
             // therefore using grayscale AA.
-            //
-            // FIXME: it should also be possible to promote if the layer can
-            // still use LCD text when promoted, but detecting when the
-            // compositor can do this is tricky. Currently, the layer must be
-            // both opaque and may only have an integer translation as its
-            // transform. Both opacity and screen space transform are inherited
-            // properties, so this cannot be determined from local information.
             layer->getScrollableArea()->updateNeedsCompositedScrolling(PaintLayerScrollableArea::IgnoreLCDText);
             if (layer->needsCompositedScrolling())
                 reasonsToComposite |= CompositingReasonOverflowScrollingTouch;