doc: Changed go/ category etc. to topic/

Per instructions from DD and JF, changing the top-level go/
directory to topic/ ; as a result, I'm going into AK's recent CLs
(in which she added infrastructure for the new go/ directory)
and changing those too.

See first comment for doc stage location.

bug: 28558659
Change-Id: Iaa10f1a9f7477b00f6bfaa748039d146dfb292fe
diff --git a/tools/droiddoc/templates-sdk-dev/head_tag.cs b/tools/droiddoc/templates-sdk-dev/head_tag.cs
index 1839df5..9145b66 100644
--- a/tools/droiddoc/templates-sdk-dev/head_tag.cs
+++ b/tools/droiddoc/templates-sdk-dev/head_tag.cs
@@ -6,7 +6,7 @@
     <meta name="top_category" value="<?cs
       if:ndk ?>ndk<?cs
       elif:(guide||develop||training||reference||tools||sdk||google||reference.gms||reference.gcm||samples) ?>develop<?cs
-      elif:(go||libraries) ?>develop<?cs
+      elif:(topic||libraries) ?>develop<?cs
       elif:(distribute||googleplay||essentials||users||engage||monetize||disttools||stories||analyze) ?>distribute<?cs
       elif:(design||vision||material||patterns||devices||designdownloads) ?>design<?cs
       elif:(about||versions||wear||tv||auto) ?>about<?cs
@@ -35,7 +35,7 @@
             if:(samplesDocPage&&!samplesProjectIndex) ?> samples-docpage<?cs /if ?><?cs
           else ?>none<?cs set:dac_subcategory_set = #0 ?><?cs /if ?><?cs
         elif:(google||reference.gms||reference.gcm) ?>google<?cs
-        elif:(go||libraries) ?><?cs
+        elif:(topic||libraries) ?><?cs
           if:libraries ?>libraries<?cs
           else ?>none<?cs set:dac_subcategory_set = #0 ?><?cs /if ?><?cs
         elif:(distribute||googleplay||essentials||users||engage||monetize||disttools||stories||analyze) ?><?cs
@@ -73,7 +73,7 @@
             elif:sdk ?>/tools<?cs
             elif:samples ?>/samples<?cs /if ?><?cs
           elif:(google||reference.gms||reference.gcm) ?>/google<?cs
-          elif:(go||libraries) ?>/go<?cs
+          elif:(topic||libraries) ?>/topic<?cs
             if:libraries ?>/libraries<?cs /if ?><?cs
           elif:(distribute||googleplay||essentials||users||engage||monetize||disttools||stories||analyze) ?>/distribute<?cs
             if:googleplay ?>/googleplay<?cs