Allow package blacklisting to be done via a file checked into the depot. By default this is disabled.

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MOS_MIGRATED_REVID=107644420
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/SkyFunctions.java b/src/main/java/com/google/devtools/build/lib/skyframe/SkyFunctions.java
index b041211..3ed5488 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/SkyFunctions.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/SkyFunctions.java
@@ -51,6 +51,8 @@
       SkyFunctionName.create("PREPARE_DEPS_OF_PATTERN");
   public static final SkyFunctionName PREPARE_DEPS_OF_TARGETS_UNDER_DIRECTORY =
       SkyFunctionName.create("PREPARE_DEPS_OF_TARGETS_UNDER_DIRECTORY");
+  public static final SkyFunctionName BLACKLISTED_PACKAGE_PREFIXES =
+      SkyFunctionName.create("BLACKLISTED_PACKAGE_PREFIXES");
   public static final SkyFunctionName TEST_SUITE_EXPANSION =
       SkyFunctionName.create("TEST_SUITE_EXPANSION");
   public static final SkyFunctionName TESTS_IN_SUITE = SkyFunctionName.create("TESTS_IN_SUITE");