Moving the checkVars pass to before the later transpilation step

(rollforward of cl/99291555)
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=99420916

Author: blickly

src/com/google/javascript/jscomp/DefaultPassConfig.java

@@ -289,6 +289,10 @@ protected List<PassFactory> getChecks() {
       checks.add(createSyntheticBlocks);
     }
 
+    if (!options.skipNonTranspilationPasses) {
+      checks.add(checkVars);
+    }
+
     // Late ES6 transpilation.
     // Includes ES6 features that are best handled natively by the compiler.
     // As we convert more passes to handle these features, we will be moving the transpilation
@@ -317,8 +321,6 @@ protected List<PassFactory> getChecks() {
 
     // End of ES6 transpilation passes.
 
-    checks.add(checkVars);
-
     if (options.inferConsts) {
       checks.add(inferConsts);
     }