Revert "Revert "Remove UTF-8 BOM from source files""

This reverts commit 0b3c460.

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

@@ -52,6 +52,7 @@
  */
 public class SourceFile implements StaticSourceFile, Serializable {
   private static final long serialVersionUID = 1L;
+  private static final String UTF8_BOM = String.format("%c", CommandLineRunner.UTF8_BOM_CODE);
 
   /** A JavaScript source code provider.  The value should
    * be cached so that the source text stays consistent throughout a single
@@ -169,7 +170,15 @@ String getCodeNoCache() {
   }
 
   private void setCode(String sourceCode) {
-    code = sourceCode;
+    this.setCode(sourceCode, false);
+  }
+
+  private void setCode(String sourceCode, boolean removeUtf8Bom) {
+    if (removeUtf8Bom && sourceCode != null && sourceCode.startsWith(UTF8_BOM)) {
+      code = sourceCode.substring(UTF8_BOM.length());
+    } else {
+      code = sourceCode;
+    }
   }
 
   public String getOriginalPath() {
@@ -543,7 +552,7 @@ public synchronized String getCode() throws IOException {
 
       if (cachedCode == null) {
         cachedCode = Files.toString(file, this.getCharset());
-        super.setCode(cachedCode);
+        super.setCode(cachedCode, this.getCharset() == StandardCharsets.UTF_8);
       }
       return cachedCode;
     }
@@ -636,7 +645,7 @@ public synchronized String getCode() throws IOException {
 
       if (cachedCode == null) {
         cachedCode = Resources.toString(url, this.getCharset());
-        super.setCode(cachedCode);
+        super.setCode(cachedCode, this.getCharset() == StandardCharsets.UTF_8);
       }
       return cachedCode;
     }