Disable CoalesceVariables in ES6-out mode.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=168760650

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

@@ -878,12 +878,11 @@ protected List<PassFactory> getOptimizations() {
       if (options.foldConstants) {
         passes.add(peepholeOptimizationsOnce);
       }
-    } else {
-      // Passes after this point can no longer depend on normalized AST
-      // assumptions.
-      passes.add(markUnnormalized);
     }
 
+    // Passes after this point can no longer depend on normalized AST assumptions.
+    passes.add(markUnnormalized);
+
     if (options.collapseVariableDeclarations) {
       passes.add(exploitAssign);
       passes.add(collapseVariableDeclarations);
@@ -2815,7 +2814,8 @@ protected CompilerPass create(AbstractCompiler compiler) {
 
         @Override
         protected FeatureSet featureSet() {
-          return ES8_MODULES;
+          // TODO(b/65688660): Switch to ES8_MODULES when b/65688660 is fixed.
+          return ES5;
         }
       };