Add support for multiple html directories to droiddoc.

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

Change-Id: I5d4b2432aa78b0b3559daacedfb7a29675701f33
diff --git a/tools/droiddoc/src/DroidDoc.java b/tools/droiddoc/src/DroidDoc.java
index 4e9d6b1..34a0c03 100644
--- a/tools/droiddoc/src/DroidDoc.java
+++ b/tools/droiddoc/src/DroidDoc.java
@@ -122,7 +122,7 @@
                 sampleCodes.add(new SampleCode(a[1], a[2], a[3]));
             }
             else if (a[0].equals("-htmldir")) {
-                ClearPage.htmlDir = a[1];
+                ClearPage.htmlDirs.add(a[1]);
             }
             else if (a[0].equals("-title")) {
                 DroidDoc.title = a[1];
@@ -224,7 +224,7 @@
             }
 
             // HTML Pages
-            if (ClearPage.htmlDir != null) {
+            if (!ClearPage.htmlDirs.isEmpty()) {
                 writeHTMLPages();
             }
 
@@ -233,7 +233,7 @@
 
             // Packages Pages
             writePackages(javadocDir
-                            + (ClearPage.htmlDir!=null
+                            + (!ClearPage.htmlDirs.isEmpty()
                                 ? "packages" + htmlExtension
                                 : "index" + htmlExtension));
 
@@ -575,11 +575,13 @@
 
     public static void writeHTMLPages()
     {
-        File f = new File(ClearPage.htmlDir);
-        if (!f.isDirectory()) {
-            System.err.println("htmlDir not a directory: " + ClearPage.htmlDir);
+        for (String htmlDir : ClearPage.htmlDirs) {
+            File f = new File(htmlDir);
+            if (!f.isDirectory()) {
+                System.err.println("htmlDir not a directory: " + htmlDir);
+            }
+            writeDirectory(f, "");
         }
-        writeDirectory(f, "");
     }
 
     public static void writeLists()