Fetch the protocol from Chrome itself when possible

Since 60.0.3097.0 Chrome provides a `/json/protocol` endpoint by which it
exposes the protocol.

https://bugs.chromium.org/p/chromium/issues/detail?id=538300#c10

This finally allows to properly close #10.

README.md

@@ -352,8 +352,8 @@ This behavior can be changed by setting the `remote` option to `true`
 upon [connection](#cdpoptions-callback), in which case the remote instance is
 *asked* to provide its own protocol descriptor.
 
-Currently Chrome is not able to do that (see [#10]), so the protocol descriptor
-is fetched from the proper [source repository].
+Chrome < 60.0.3097.0 is not able to do that, so in that case the protocol
+descriptor is fetched from the source repository.
 
 To override the above behavior there are basically three options:
 
@@ -367,8 +367,6 @@ To override the above behavior there are basically three options:
   fetched with `npm install`).
 
 [local version]: lib/protocol.json
-[#10]: https://github.com/cyrus-and/chrome-remote-interface/issues/10
-[source repository]: https://chromium.googlesource.com/chromium/src/+/master/third_party/WebKit/Source/
 
 Browser usage
 -------------

lib/devtools.js

@@ -28,7 +28,15 @@ module.exports.Protocol = promisesWrapper(function (options, callback) {
         // use the proper protocol fetcher
         let fetcher;
         if (browser.match(/^(Headless)?Chrome\//)) {
-            fetcher = fetchFromChromeRepo;
+            // https://bugs.chromium.org/p/chromium/issues/detail?id=538300#c10
+            const firstJsonProtocolVersion = '60.0.3097.0';
+            const firstJsonProtocolBuild = explodeChromeVersion(firstJsonProtocolVersion)[2];
+            const chromeBuild = explodeChromeVersion(info.Browser.split('/')[1])[2];
+            if (chromeBuild < firstJsonProtocolBuild) {
+                fetcher = fetchFromChromeRepo;
+            } else {
+                fetcher = fetchFromHttpEndpoint;
+            }
         } else if (browser.match(/^Microsoft Edge /)) {
             fetcher = fetchFromHttpEndpoint;
         } else if (browser.match(/^node.js\//)) {
@@ -144,15 +152,16 @@ function promisesWrapper(func) {
     };
 }
 
+function explodeChromeVersion(v) {
+    return v.split('.').map(function (x) {
+        return parseInt(x);
+    });
+}
+
 // callback(err, descriptor)
 // XXX this function needs a proper refactor but the inconsistency of the
 // fetching process makes it useless for now
 function fetchFromChromeRepo(options, info, callback) {
-    function explodeVersion(v) {
-        return v.split('.').map(function (x) {
-            return parseInt(x);
-        });
-    }
     // attempt to fetch the protocol directly from the Chromium repository
     // according to the current version
     //
@@ -169,10 +178,10 @@ function fetchFromChromeRepo(options, info, callback) {
     } else {
         const lastBeforeSplitChromeVersion = '53.0.2758.1'; // before the split (https://crbug.com/580337)
         const lastBeforeV8ChromeVersion = '55.0.2854.3'; // before using the JSON from the V8 repo
-        const chromeVersion = explodeVersion(info.Browser.split('/')[1]);
-        // according to https://www.chromium.org/developers/version-numbers
-        const beforeSplit = (chromeVersion[2] <= explodeVersion(lastBeforeSplitChromeVersion)[2]); // patch not meaningful
-        const beforeFromV8 = (chromeVersion[2] <= explodeVersion(lastBeforeV8ChromeVersion)[2]); // patch not meaningful
+        const chromeVersion = explodeChromeVersion(info.Browser.split('/')[1]);
+        // according to https://www.chromium.org/developers/version-numbers (patch not meaningful)
+        const beforeSplit = (chromeVersion[2] <= explodeChromeVersion(lastBeforeSplitChromeVersion)[2]);
+        const beforeFromV8 = (chromeVersion[2] <= explodeChromeVersion(lastBeforeV8ChromeVersion)[2]);
         if (beforeSplit) {
             urls = [`https://chromium.googlesource.com/chromium/src/+/${hash}/third_party/WebKit/Source/devtools/protocol.json?format=TEXT`];
         } else if (beforeFromV8) {