Separate @viewport from other RuleSet construction.

third_party/WebKit/Source/core/dom/DocumentStyleSheetCollection.cpp

Index: third_party/WebKit/Source/core/dom/DocumentStyleSheetCollection.cpp
diff --git a/third_party/WebKit/Source/core/dom/DocumentStyleSheetCollection.cpp b/third_party/WebKit/Source/core/dom/DocumentStyleSheetCollection.cpp
index 8e163a71a496a39f50e18d769632fd26e6d686de..da691ab664931fcfa25e2d705eda46a7abe7f0fe 100644
--- a/third_party/WebKit/Source/core/dom/DocumentStyleSheetCollection.cpp
+++ b/third_party/WebKit/Source/core/dom/DocumentStyleSheetCollection.cpp
@@ -29,6 +29,7 @@
 #include "core/dom/DocumentStyleSheetCollection.h"
 
 #include "core/css/resolver/StyleResolver.h"
+#include "core/css/resolver/ViewportStyleResolver.h"
 #include "core/dom/Document.h"
 #include "core/dom/DocumentStyleSheetCollector.h"
 #include "core/dom/ProcessingInstruction.h"
@@ -130,6 +131,30 @@ void DocumentStyleSheetCollection::updateActiveStyleSheets(
   collection->dispose();
 }
 
+void DocumentStyleSheetCollection::updateViewport() {
+  ViewportStyleResolver& resolver =
+      document().styleEngine().ensureViewportStyleResolver();
+  resolver.reset();
+  resolver.collectViewportRulesFromUASheets();
+
+  if (RuntimeEnabledFeatures::cssViewportEnabled()) {
+    for (Node* node : m_styleSheetCandidateNodes) {
+      StyleSheetCandidate candidate(*node);
+
+      if (candidate.isImport())
+        continue;
+      StyleSheet* sheet = candidate.sheet();
+      if (!sheet)
+        continue;
+      if (!candidate.canBeActivated(
+              document().styleEngine().preferredStylesheetSetName()))
+        continue;
+      resolver.collectViewportRulesFromAuthorSheet(*toCSSStyleSheet(sheet));
+    }
+  }
+  resolver.resolve();
+}
+
 DEFINE_TRACE_WRAPPERS(DocumentStyleSheetCollection) {
   for (auto sheet : m_styleSheetsForStyleSheetList) {
     visitor->traceWrappers(sheet);