PNaCl documentation: clarify vector alignment, and update navigation

chrome/common/extensions/docs/templates/json/chrome_sidenav.json

Index: chrome/common/extensions/docs/templates/json/chrome_sidenav.json
diff --git a/chrome/common/extensions/docs/templates/json/chrome_sidenav.json b/chrome/common/extensions/docs/templates/json/chrome_sidenav.json
index 312affa4bc46b785cfb36dca6aa302c59e817a8d..f14348251eb130f345c18dd1a4261377f09eee14 100644
--- a/chrome/common/extensions/docs/templates/json/chrome_sidenav.json
+++ b/chrome/common/extensions/docs/templates/json/chrome_sidenav.json
@@ -861,6 +861,10 @@
                 "href": "/native-client/reference/pnacl-bitcode-abi"
               },
               {
+                "title": "PNaCl Undefined Behavior",
+                "href": "/native-client/reference/pnacl-undefined-behavior"
+              },
+              {
                 "title": "PNaCl C/C++ Language Support",
                 "href": "/native-client/reference/pnacl-c-cpp-language-support"
               },
@@ -871,6 +875,10 @@
                     {
                       "title": "ARM 32-bit Sandbox",
                       "href": "/native-client/reference/sandbox_internals/arm-32-bit-sandbox"
+                    },
+                    {
+                      "title": "x86-64 Sandbox",
+                      "href": "/native-client/reference/sandbox_internals/x86-64-sandbox"
                     }
                 ]
               }