Bug 1565980. Force wmode 'gpu' to 'direct'. r=jmathies

This fixes wmode='gpu' with WebRender.

Differential Revision: https://phabricator.services.mozilla.com/D39420

--HG--
extra : moz-landing-system : lando

dom/plugins/ipc/PluginModuleParent.cpp

@@ -2046,7 +2046,8 @@ static void ForceDirect(nsTArray<nsCString>& names,
   NS_NAMED_LITERAL_CSTRING(directAttributeValue, "direct");
   auto wmodeAttributeIndex = names.IndexOf(wmodeAttributeName, 0, comparator);
   if (wmodeAttributeIndex != names.NoIndex) {
-    if (values[wmodeAttributeIndex].EqualsLiteral("window")) {
+    if (values[wmodeAttributeIndex].EqualsLiteral("window") ||
+        values[wmodeAttributeIndex].EqualsLiteral("gpu")) {
       values[wmodeAttributeIndex].Assign(directAttributeValue);
     }
   } else {