DCHECK that CSSVariableResolver isn't used when CSSCascade is on

Change-Id: Id8b9b3ede1a3589ee8ce19afa0ca84db303a7c4b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2132196Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Anders Hartvoll Ruud <andruud@chromium.org>
Cr-Commit-Position: refs/heads/master@{#756073}

third_party/blink/renderer/core/css/resolver/css_variable_resolver.cc

@@ -536,6 +536,9 @@ CSSVariableResolver::CSSVariableResolver(const StyleResolverState& state)
     : state_(state),
       inherited_variables_(state.Style()->InheritedVariables()),
       non_inherited_variables_(state.Style()->NonInheritedVariables()),
-      registry_(state.GetDocument().GetPropertyRegistry()) {}
+      registry_(state.GetDocument().GetPropertyRegistry()) {
+  DCHECK(!RuntimeEnabledFeatures::CSSCascadeEnabled())
+      << "Use StyleCascade instead";
+}
 
 }  // namespace blink

third_party/blink/renderer/core/css/resolver/css_variable_resolver_test.cc

@@ -26,6 +26,7 @@
 #include "third_party/blink/renderer/core/style/computed_style.h"
 #include "third_party/blink/renderer/core/testing/page_test_base.h"
 #include "third_party/blink/renderer/platform/heap/heap.h"
+#include "third_party/blink/renderer/platform/testing/runtime_enabled_features_test_helpers.h"
 #include "third_party/blink/renderer/platform/wtf/text/string_builder.h"
 
 namespace blink {
@@ -43,8 +44,11 @@ static const Color kTestColor = Color(255, 0, 0);
 
 }  // namespace
 
-class CSSVariableResolverTest : public PageTestBase {
+class CSSVariableResolverTest : public PageTestBase,
+                                private ScopedCSSCascadeForTest {
  public:
+  CSSVariableResolverTest() : ScopedCSSCascadeForTest(false) {}
+
   void SetUp() override {
     PageTestBase::SetUp();