Add #toString for ContainingPackageLookupValue.

PiperOrigin-RevId: 220845686
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/ContainingPackageLookupValue.java b/src/main/java/com/google/devtools/build/lib/skyframe/ContainingPackageLookupValue.java
index f9cfb82..7ab319c 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/ContainingPackageLookupValue.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/ContainingPackageLookupValue.java
@@ -13,6 +13,7 @@
 // limitations under the License.
 package com.google.devtools.build.lib.skyframe;
 
+import com.google.common.base.MoreObjects;
 import com.google.common.base.Preconditions;
 import com.google.common.collect.Interner;
 import com.google.devtools.build.lib.cmdline.Label;
@@ -127,6 +128,11 @@
     public Root getContainingPackageRoot() {
       throw new IllegalStateException();
     }
+
+    @Override
+    public String toString() {
+      return getClass().getName();
+    }
   }
 
   /** A successful lookup value. */
@@ -174,5 +180,13 @@
     public int hashCode() {
       return containingPackage.hashCode();
     }
+
+    @Override
+    public String toString() {
+      return MoreObjects.toStringHelper(this)
+          .add("containingPackage", containingPackage)
+          .add("containingPackageRoot", containingPackageRoot)
+          .toString();
+    }
   }
 }