Fix property comparison in CSSAnimations.

Addresses regression introduced in:
https://chromium-review.googlesource.com/c/chromium/src/+/2369433

ComputedStyleUtils::ComputedPropertyValue can return a null value if
the value cannot be parsed, which leads to a potential null pointer
dereference.

Bug: 1126364
Change-Id: I31a74283a4cbfe9c6875fb9c832d6085ab21ae39
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2517044Reviewed-by: Xida Chen <xidachen@chromium.org>
Commit-Queue: Kevin Ellis <kevers@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823978}

third_party/blink/renderer/core/animation/css/css_animations.cc

@@ -525,9 +525,12 @@ bool ComputedValuesEqual(const PropertyHandle& property,
         ComputedStyleUtils::ComputedPropertyValue(property.GetCSSProperty(), a);
     const CSSValue* b_val =
         ComputedStyleUtils::ComputedPropertyValue(property.GetCSSProperty(), b);
-    DCHECK(a_val);
-    DCHECK(b_val);
-    return *a_val == *b_val;
+    // Computed values can be null if not able to parse.
+    if (a_val && b_val)
+      return *a_val == *b_val;
+    // Fallback to the zoom-unaware comparator if either value could not be
+    // parsed.
+    return CSSPropertyEquality::PropertiesEqual(property, a, b);
   }
 }