[NaCl SDK Docs] Only generate one top-level <section> element.

native_client_sdk/src/doc/_sphinxext/chromesite_builder.py

Index: native_client_sdk/src/doc/_sphinxext/chromesite_builder.py
diff --git a/native_client_sdk/src/doc/_sphinxext/chromesite_builder.py b/native_client_sdk/src/doc/_sphinxext/chromesite_builder.py
index c44b3f757793e6eb070aa124bcacbd904e79662f..6c133bff417f65418146224ecdbbe160798fa4fd 100644
--- a/native_client_sdk/src/doc/_sphinxext/chromesite_builder.py
+++ b/native_client_sdk/src/doc/_sphinxext/chromesite_builder.py
@@ -103,11 +103,13 @@ class ChromesiteHTMLTranslator(HTMLTranslator):
   def visit_section(self, node):
     # chromesite needs <section> instead of <div class='section'>
     self.section_level += 1
-    self.body.append(self.starttag(node, 'section'))
+    if self.section_level == 1:
+      self.body.append(self.starttag(node, 'section'))
 
   def depart_section(self, node):
+    if self.section_level == 1:
+      self.body.append('</section>')
     self.section_level -= 1
-    self.body.append('</section>')
 
   def visit_image(self, node):
     # Paths to images in .rst sources should be absolute. This visitor does the