Chrome CLI Runner to facilitate an async exit.

* We now load a headless chrome platform ONLY if Chrome CLIRunner is being used
* We inhibit a default exit from CDP interface if Kernel#exit hasn't been called
  (and opal-platform has been loaded)
* We modify Kernel#exit to run a special alert message to communicate with
  Chrome CDP interface (we would have sent an exception, but it doesn't
  bubble in the async mess - perhaps it will once we migrate to PromiseV2)

Thanks to Brandon Gastelo for spotting this bug.

Ref: opal-rspec#89

lib/opal/cli_runners/chrome.rb

@@ -80,6 +80,7 @@ def prepare_files_in(dir)
             <meta charset='utf-8'>
             <script src='./source-map-support.js'></script>
             <script>
+            window.opalheadlesschrome = true;
             sourceMapSupport.install({
               retrieveSourceMap: function(path) {
                 return path.endsWith('/index.#{ext}') ? {

lib/opal/cli_runners/chrome_cdp_interface.rb

@@ -106,17 +106,34 @@
           else
             `Page.handleJavaScriptDialog({accept: false})`
           end
+        elsif `dialog.type` == 'alert' && `dialog.message` == 'opalheadlesschromeexit'
+          # A special case of an alert with a magic string "opalheadlesschromeexit".
+          # This denotes that `Kernel#exit` has been called. We would have rather used
+          # an exception here, but they don't bubble sometimes.
+          %x{
+            Page.handleJavaScriptDialog({accept: true});
+            Runtime.evaluate({ expression: "window.OPAL_EXIT_CODE" }).then(function(output) {
+              client.close();
+              if (typeof(output.result) !== "undefined" && output.result.type === "number") {
+                process.exit(output.result.value);
+              } else {
+                process.exit(0);
+              }
+            });
+          }
         end
       }
     });
 
     Page.loadEventFired(() => {
       Runtime.evaluate({ expression: "window.OPAL_EXIT_CODE" }).then(function(output) {
-        client.close();
-
         if (typeof(output.result) !== "undefined" && output.result.type === "number") {
+          client.close();
           process.exit(output.result.value);
+        } else if (typeof(output.result) !== "undefined" && output.result.type === "string" && output.result.value === "noexit") {
+          // do nothing, we have headless chrome support enabled and there are most probably async events awaiting
         } else {
+          client.close();
           process.exit(0);
         }
       })

stdlib/headless_chrome.rb

@@ -1,11 +1,15 @@
 %x{
+  // Inhibit the default exit behavior
+  window.OPAL_EXIT_CODE = "noexit";
+
   Opal.exit = function(code) {
-    // You can't exit from the browser.
     // The first call to Opal.exit should save an exit code.
     // All next invocations must be ignored.
+    // Then we send an event to Chrome CDP Interface that we are finished
 
-    if (typeof(window.OPAL_EXIT_CODE) === "undefined") {
+    if (window.OPAL_EXIT_CODE === "noexit") {
       window.OPAL_EXIT_CODE = code;
+      window.alert("opalheadlesschromeexit");
     }
   }
 }

stdlib/opal-platform.rb

@@ -3,7 +3,7 @@
 browser         = `typeof(document) !== "undefined"`
 node            = `typeof(process) !== "undefined" && process.versions && process.versions.node`
 nashorn         = `typeof(Java) !== "undefined" && Java.type`
-headless_chrome = `typeof(navigator) !== "undefined" && /\bHeadlessChrome\//.test(navigator.userAgent)`
+headless_chrome = `typeof(opalheadlesschrome) !== 'undefined'`
 gjs             = `typeof(window) !== "undefined" && typeof(GjsFileImporter) !== 'undefined'`
 quickjs         = `typeof(window) === "undefined" && typeof(__loadScript) !== 'undefined'`
 opal_miniracer  = `typeof(opalminiracer) !== 'undefined'`