Don't crash when animating with CSSCascade disabled

Running without the CSSCascade flag doesn't work anymore, since we
hit a DCHECK. We're not supposed to calculate the animation update more
than once, and with CSSCascade disabled it can potentially already have
happened once we reach ApplyAnimatedStandardProperties. This CL re-
introduces an if-check that was removed in [1] to fix the issue.

[1] https://chromium-review.googlesource.com/c/chromium/src/+/2064248

Change-Id: I340f31543f63ed05a6a033ece0779ffaa8d57e28
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2132400Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Anders Hartvoll Ruud <andruud@chromium.org>
Cr-Commit-Position: refs/heads/master@{#756062}

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

@@ -1357,7 +1357,10 @@ bool StyleResolver::ApplyAnimatedStandardProperties(
   if (!HasAnimationsOrTransitions(state))
     return false;
 
-  CalculateAnimationUpdate(state);
+  if (!state.IsAnimationInterpolationMapReady() ||
+      RuntimeEnabledFeatures::CSSCascadeEnabled()) {
+    CalculateAnimationUpdate(state);
+  }
 
   CSSAnimations::CalculateCompositorAnimationUpdate(
       state.AnimationUpdate(), animating_element, element, *state.Style(),

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

@@ -12,6 +12,7 @@
 #include "third_party/blink/renderer/core/dom/shadow_root.h"
 #include "third_party/blink/renderer/core/dom/text.h"
 #include "third_party/blink/renderer/core/testing/page_test_base.h"
+#include "third_party/blink/renderer/platform/testing/runtime_enabled_features_test_helpers.h"
 
 namespace blink {
 
@@ -126,6 +127,24 @@ TEST_F(StyleResolverTest, BasePresentIfFontRelativeUnitsAbsent) {
   EXPECT_TRUE(animations.BaseComputedStyle());
 }
 
+TEST_F(StyleResolverTest, NoCrashWhenAnimatingWithoutCascade) {
+  ScopedCSSCascadeForTest scoped_cascade(false);
+
+  GetDocument().documentElement()->setInnerHTML(R"HTML(
+    <style>
+      @keyframes test {
+        from { width: 10px; }
+        to { width: 20px; }
+      }
+      div {
+        animation: test 1s;
+      }
+    </style>
+    <div id="div">Test</div>
+  )HTML");
+  UpdateAllLifecyclePhasesForTest();
+}
+
 class StyleResolverFontRelativeUnitTest
     : public testing::WithParamInterface<const char*>,
       public StyleResolverTest {};