Fix left-side navigation for top-level pages

And don't break presubmit!
Basically, the change I put in previously that kind of fixed extensions redirects
actually meant presubmit would fail.
So I've gone and put in a real fix.

I also updated the redirects.json files in these GitHub repos for this to work: devtools, multi-device, and store.

Thanks, Ben, for your help.

Review URL: https://codereview.chromium.org/883963002

Cr-Commit-Position: refs/heads/master@{#313575}

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

@@ -4,11 +4,11 @@
     "items": [
       {
         "title": "Learn Basics",
-        "href": "/devtools/index",
+        "href": "/devtools",
         "items": [
           {
             "title": "Overview",
-            "href": "/devtools/index"
+            "href": "/devtools"
           },
           {
             "title": "Development Workflow",
@@ -195,11 +195,11 @@
     "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",
@@ -532,11 +532,11 @@
       },
       {
         "title": "Extensions",
-        "href": "/extensions/index",
+        "href": "/extensions",
         "items": [
           {
             "title": "Learn Basics",
-            "href": "/extensions/index",
+            "href": "/extensions",
             "items": [
               {
                 "title": "Overview",
@@ -705,11 +705,11 @@
       },
       {
         "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",
@@ -937,11 +937,11 @@
       },
       {
         "title": "Store",
-        "href": "/webstore/index",
+        "href": "/webstore",
         "items": [
           {
             "title": "Distribution Overview",
-            "href": "/webstore/index"
+            "href": "/webstore"
           },
           {
             "title": "What Is the Chrome Web Store?",

chrome/common/extensions/docs/templates/public/extensions/redirects.json

@@ -6,5 +6,6 @@
   "experimental.systemInfo_storage": "system_storage",
   "experimental_systemInfo_storage": "system_storage",
   "systemInfo_cpu": "system_cpu",
-  "systemInfo_memory": "system_memory"
+  "systemInfo_memory": "system_memory",
+  "index": "."
 }

chrome/common/extensions/docs/templates/public/redirects.json

 {
   "": "/home",
-  "apps": "/apps/about_apps",
-  "native-client": "/native-client/index",
-  "extensions": "/extensions/index",
-  "devtools": "devtools/index",
-  "multidevice": "multidevice/index",
-  "webstore": "/webstore/index"
+  "apps": "/apps/about_apps"
 }

native_client_sdk/doc_generated/redirects.json

+{
+  "index": "."
+}