Docserver: Make the .html extension unnecessary for content pages, for example,

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

 // === Overview ===
 //
 // This file configures where to find and how to serve content in the docserver.
 // It's the most fundamentally important file in all of the docserver.
 //
 // === Format ===
 //
 // Each entry declares a rule with:
 //  * An arbitrary identifier key e.g. "cr-extensions-examples".
 //  * What URL the rule should be invoked with, given by "serveFrom", e.g.
@@ skipping 27 matching lines @@
 //  * "supportsTemplates" indicates whether HTML files should be treated and
 //    renderered as templates, versus just plain text. Complex documentation
 //    which interacts with docserver features (like API listing) need to set
 //    this to true. Otherwise, it's safer and more efficient to omit it.
 
 {
   "cr-chrome-docs-home": {
     "chromium": {
       "dir": "chrome/docs"
     },
+    "defaultExtensions": [".html", ".md"],
     "serveFrom": "home",
     "supportsTemplates": true
   },
   "cr-extensions-examples": {
     "chromium": {
       "dir": "chrome/common/extensions/docs/examples"
     },
     "serveFrom": "extensions/examples",
     "supportsZip": true
   },
   "cr-public": {
     "chromium": {
       "dir": "chrome/common/extensions/docs/templates/public"
     },
+    "defaultExtensions": [".html", ".md"],
     "serveFrom": "",
     "supportsTemplates": true
   },
   "cr-static": {
     "chromium": {
       "dir": "chrome/common/extensions/docs/static"
     },
     "serveFrom": "static"
   },
   "cr-native-client": {
     "chromium": {
       "dir": "native_client_sdk/doc_generated"
     },
+    "defaultExtensions": [".html", ".md"],
     "serveFrom": "native-client",
     "supportsTemplates": true
   },
   "devtools-docs": {
     "gcs": {
       "bucket": "gs://chromedocs-devtools"
     },
     "serveFrom": "devtools",
     "supportsTemplates": true
   },
   "multidevice-docs": {
     "gcs": {
       "bucket": "gs://chromedocs-multidevice"
     },
     "serveFrom": "multidevice",
     "supportsTemplates": true
   },
   "webstore-docs": {
     "gcs": {
       "bucket": "gs://chromedocs-webstore"
     },
     "serveFrom": "webstore",
     "supportsTemplates": true
   }
 }