Replace String[] with String... in a few CompilerTestCase helper meth…

…ods.

The new signature is compatible with existing callsites, but gives additional flexibility when writing test code.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=209058337

test/com/google/javascript/jscomp/CompilerTestCase.java

@@ -2156,7 +2156,7 @@ protected static Expected expected(String srcText) {
     return new Expected(maybeCreateSources("expected",  srcText));
   }
 
-  protected static Expected expected(String[] srcTexts) {
+  protected static Expected expected(String... srcTexts) {
     return new Expected(createSources("expected", srcTexts));
   }
 
@@ -2189,7 +2189,7 @@ protected static Externs externs(String externSrc) {
     return new Externs(maybeCreateSources("externs",  externSrc));
   }
 
-  protected static Externs externs(String[] srcTexts) {
+  protected static Externs externs(String... srcTexts) {
     return new Externs(createSources("externs", srcTexts));
   }