Remove spurious leading space from AutoValue_Foo generated source.

Closes #623
Fixes #622

RELNOTES=n/a

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=192124429

value/src/main/java/com/google/auto/value/processor/AutoValueProcessor.java

@@ -204,6 +204,7 @@ void processType(TypeElement type) {
     String subclass = generatedSubclassName(type, subclassDepth);
     vars.subclass = TypeSimplifier.simpleNameOf(subclass);
     vars.isFinal = (subclassDepth == 0);
+    vars.modifiers = vars.isFinal ? "final " : "abstract ";
 
     String text = vars.toText();
     text = TypeEncoder.decode(text, processingEnv, vars.pkg, type.asType());

value/src/main/java/com/google/auto/value/processor/AutoValueTemplateVars.java

@@ -73,6 +73,12 @@ class AutoValueTemplateVars extends AutoValueOrOneOfTemplateVars {
    */
   Boolean isFinal = false;
 
+  /**
+   * The modifiers (for example {@code final} or {@code abstract}) for the generated subclass,
+   * followed by a space if they are not empty.
+   */
+  String modifiers;
+
   /**
    * The name of the builder type as it should appear in source code, or empty if there is no
    * builder type. If class {@code Address} contains {@code @AutoValue.Builder} class Builder

value/src/main/java/com/google/auto/value/processor/autovalue.vm

@@ -44,7 +44,7 @@ $a
 #else
 // Generated by com.google.auto.value.processor.AutoValueProcessor
 #end
-#if ($isFinal) final #else abstract #end class $subclass$formalTypes extends $origClass$actualTypes {
+${modifiers}class $subclass$formalTypes extends $origClass$actualTypes {
 
 ## Fields