Bug 1469176: Load svg.css upfront. r=jwatt

Test Plan: Covered by existing tests.

Reviewers: jwatt

Reviewed By: jwatt

Bug #: 1469176

Differential Revision: https://phabricator.services.mozilla.com/D1762

dom/svg/SVGSVGElement.cpp

@@ -495,14 +495,6 @@ SVGSVGElement::BindToTree(nsIDocument* aDocument,
                                               aCompileEventHandlers);
   NS_ENSURE_SUCCESS(rv,rv);
 
-  if (nsIDocument* doc = GetComposedDoc()) {
-    // Setup the style sheet during binding, not element construction, because
-    // we could move the root SVG element from the document that created it to
-    // another document.
-    auto cache = nsLayoutStylesheetCache::Singleton();
-    doc->EnsureOnDemandBuiltInUASheet(cache->SVGSheet());
-  }
-
   if (mTimedDocumentRoot && smilController) {
     rv = mTimedDocumentRoot->SetParent(smilController);
     if (mStartAnimationOnBindToTree) {

layout/base/nsDocumentViewer.cpp

@@ -2514,6 +2514,11 @@ nsDocumentViewer::CreateStyleSet(nsIDocument* aDocument)
     styleSet->PrependStyleSheet(SheetType::Agent, sheet);
   }
 
+  sheet = cache->SVGSheet();
+  if (sheet) {
+    styleSet->PrependStyleSheet(SheetType::Agent, sheet);
+  }
+
   styleSet->PrependStyleSheet(SheetType::Agent, cache->UASheet());
 
   if (nsStyleSheetService* sheetService = nsStyleSheetService::GetInstance()) {