compositor-worker: Force elements to grow a layer when a CompositorProxy is created.

Source/core/dom/Element.cpp

Index: Source/core/dom/Element.cpp
diff --git a/Source/core/dom/Element.cpp b/Source/core/dom/Element.cpp
index f6e4dda538c64b121e6ec7c0e55b5b2aae0dd389..f3a28ba17abcdcc4a8623ce6d08fbfc361cf2035 100644
--- a/Source/core/dom/Element.cpp
+++ b/Source/core/dom/Element.cpp
@@ -951,12 +951,14 @@ void Element::scrollFrameTo(const ScrollToOptions& scrollToOptions)
 
 void Element::incrementProxyCount()
 {
-    ensureElementRareData().incrementProxyCount();
+    if (ensureElementRareData().incrementProxyCount() == 1)
+        setNeedsStyleRecalc(LocalStyleChange, StyleChangeReasonForTracing::create(StyleChangeReason::CompositorProxy));
 }
 
 void Element::decrementProxyCount()
 {
-    ensureElementRareData().decrementProxyCount();
+    if (ensureElementRareData().decrementProxyCount() == 0)
+        setNeedsStyleRecalc(LocalStyleChange, StyleChangeReasonForTracing::create(StyleChangeReason::CompositorProxy));
 }
 
 IntRect Element::boundsInViewportSpace()
@@ -1651,6 +1653,9 @@ PassRefPtr<ComputedStyle> Element::styleForLayoutObject()
             style->setHasInlineTransform(inlineStyle->hasProperty(CSSPropertyTransform) || inlineStyle->hasProperty(CSSPropertyWebkitTransform));
     }
 
+    if (hasRareData() && elementRareData()->proxyCount() > 0)
+        style->setHasCompositorProxy(true);
+
     document().didRecalculateStyleForElement();
     return style.release();
 }