Fix implementation of ComputedDefault attributes on aspects, not to throw ClassCast exception.

Before the fix as soon as a ComputedDefault attribute was added to an aspect ClassCast exception was thrown.

RELNOTES: None.
PiperOrigin-RevId: 314797027
diff --git a/src/test/java/com/google/devtools/build/lib/analysis/AspectTest.java b/src/test/java/com/google/devtools/build/lib/analysis/AspectTest.java
index 60164a6..2df81ba 100644
--- a/src/test/java/com/google/devtools/build/lib/analysis/AspectTest.java
+++ b/src/test/java/com/google/devtools/build/lib/analysis/AspectTest.java
@@ -327,6 +327,15 @@
   }
 
   @Test
+  public void aspectWithComputedAttribute() throws Exception {
+    setRulesAvailableInTests(TestAspects.BASE_RULE, TestAspects.COMPUTED_ATTRIBUTE_ASPECT_RULE);
+
+    pkg("a", "rule_with_computed_deps_aspect(name='a', foo=[':b'])", "base(name='b')");
+
+    getConfiguredTarget("//a:a");
+  }
+
+  @Test
   public void ruleDependencyDeprecationWarningsAbsentDuringAspectEvaluations() throws Exception {
     setRulesAvailableInTests(TestAspects.BASE_RULE, TestAspects.ASPECT_REQUIRING_RULE);