Fix left-side navigation for top-level pages

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

 [
   {
     "title": "Devtools",
     "items": [
       {
         "title": "Learn Basics",
-        "href": "/devtools/index",
+        "href": "/devtools",
         "items": [
           {
             "title": "Overview",
-            "href": "/devtools/index"
+            "href": "/devtools"
           },
           {
             "title": "Development Workflow",
             "href": "/devtools/docs/authoring-development-workflow"
           },
           {
             "title": "Using the Console",
             "href": "/devtools/docs/console"
           },
           {
@@ skipping 166 matching lines @@
           }
         ]
       }
     ]
   },
   {
     "title": "Multi-device",
     "items": [
       {
         "title": "Getting Started",
-        "href": "/multidevice/index",
+        "href": "/multidevice",
         "items": [
           {
             "title": "Chrome for a Multi-Device World",
-            "href": "/multidevice/index"
+            "href": "/multidevice"
           },
           {
             "title": "Data Compression Proxy",
             "href": "/multidevice/data-compression"
           },
           {
             "title": "User Agents",
             "href": "/multidevice/user-agent"
           },
           {
@@ skipping 312 matching lines @@
               {
                 "title": "Stack Overflow",
                 "href": "http://stackoverflow.com/questions/tagged/google-chrome-app"
               }
             ]
           }
         ]
       },
       {
         "title": "Extensions",
-        "href": "/extensions/index",
+        "href": "/extensions",
         "items": [
           {
             "title": "Learn Basics",
-            "href": "/extensions/index",
+            "href": "/extensions",
             "items": [
               {
                 "title": "Overview",
                 "href": "/extensions/overview"
               },
               {
                 "title": "Hosting Changes",
                 "href": "/extensions/hosting_changes"
               },
               {
@@ skipping 148 matching lines @@
               {
                 "title": "Stack Overflow",
                 "href": "http://stackoverflow.com/tags/google-chrome-extension/info"
               }
             ]
           }
         ]
       },
       {
         "title": "Native Client",
-        "href": "/native-client/index",
+        "href": "/native-client",
         "items": [
           {
             "title": "Learn Basics",
-            "href": "/native-client/index",
+            "href": "/native-client",
             "items": [
               {
                 "title": "Technical Overview",
                 "href": "/native-client/overview"
               },
               {
                 "title": "NaCl and PNaCl",
                 "href": "/native-client/nacl-and-pnacl"
               }
             ]
@@ skipping 207 matching lines @@
               {
                 "title": "Security Contest Archive",
                 "href": "/native-client/community/security-contest/index"
               }
             ]
           }
         ]
       },
       {
         "title": "Store",
-        "href": "/webstore/index",
+        "href": "/webstore",
         "items": [
           {
             "title": "Distribution Overview",
-            "href": "/webstore/index"
+            "href": "/webstore"
           },
           {
             "title": "What Is the Chrome Web Store?",
             "href": "/webstore/about_webstore"
           },
           {
             "title": "What Can You Publish?",
             "href": "/webstore/overview"
           },
           {
@@ skipping 94 matching lines @@
                 "title": "Articles",
                 "href": "/webstore/articles"
               }
             ]
           }
         ]
       }
     ]
   }
 ]