Skylark: load() allows the loading of symbols via an alias.

E.g. load("/foo/bla", my_rule = "old_name") will introduce the symbol "my_rule" as an alias for "old_name".

--
MOS_MIGRATED_REVID=98933635
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/Environment.java b/src/main/java/com/google/devtools/build/lib/syntax/Environment.java
index 6c1834e..cea5ea5 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/Environment.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/Environment.java
@@ -295,16 +295,18 @@
     this.importedExtensions = importedExtensions;
   }
 
-  public void importSymbol(PathFragment extension, String symbol)
+  public void importSymbol(PathFragment extension, Identifier symbol, String nameInLoadedFile)
       throws NoSuchVariableException, LoadFailedException {
     if (!importedExtensions.containsKey(extension)) {
       throw new LoadFailedException(extension.toString());
     }
-    Object value = importedExtensions.get(extension).lookup(symbol);
+
+    Object value = importedExtensions.get(extension).lookup(nameInLoadedFile);
     if (!isSkylarkEnabled()) {
       value = SkylarkType.convertFromSkylark(value);
     }
-    update(symbol, value);
+
+    update(symbol.getName(), value);
   }
 
   /**