dd support for multiple html directories to doclava.

The goal for adding this support is to allow doclava to pull html
files both from the static content and from content generated at
build time.

Change-Id: I5d0db2c5868b93452c47cf69da93ca0a742e3400
diff --git a/src/com/google/doclava/ClearPage.java b/src/com/google/doclava/ClearPage.java
index 4bb0784..a112b7f 100644
--- a/src/com/google/doclava/ClearPage.java
+++ b/src/com/google/doclava/ClearPage.java
@@ -40,7 +40,7 @@
   private static ArrayList<String> mBundledTemplateDirs = new ArrayList<String>();
 
   public static String outputDir = "docs";
-  public static String htmlDir = null;
+  public static List<String> htmlDirs = new ArrayList<String>();
   public static String toroot = null;
 
   public static void addTemplateDir(String dir) {
@@ -85,7 +85,7 @@
   }
 
   public static void write(Data data, String templ, String filename, boolean fullPath, JSilver cs) {
-    if (htmlDir != null) {
+    if (!htmlDirs.isEmpty()) {
       data.setValue("hasindex", "true");
     }
 
@@ -112,9 +112,11 @@
     }
 
     int i = 0;
-    if (htmlDir != null) {
-      data.setValue("hdf.loadpaths." + i, htmlDir);
-      i++;
+    if (!htmlDirs.isEmpty()) {
+        for (String dir : htmlDirs) {
+          data.setValue("hdf.loadpaths." + i, dir);
+          i++;
+        }
     }
     if (mTemplateDirSet) {
       for (String dir : mTemplateDirs) {