Adds support for headless chrome embedder mojo services

headless/lib/renderer/headless_content_renderer_client.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "headless/lib/renderer/headless_content_renderer_client.h"
 
+#include "base/strings/utf_string_conversions.h"
+#include "content/public/renderer/render_frame.h"
+
 namespace headless {
 
 HeadlessContentRendererClient::HeadlessContentRendererClient() {}
 
 HeadlessContentRendererClient::~HeadlessContentRendererClient() {}
 
+void HeadlessContentRendererClient::RunScriptsAtDocumentStart(
+    content::RenderFrame* render_frame) {
+  render_frame->ExecuteJavaScript(base::UTF8ToUTF16(R"(
+      // Shim to let code use define() instead of mojo.define()
+      window.define = (function() {
+        let moduleCache = new Map();
+        return function(name, deps, factory) {
+          let promise = moduleCache.get(name);
+          if (promise === undefined) {
+            // This promise must be cached as mojo.define will only call the
+            // factory function the first time the module is defined.
+            promise = new Promise(resolve => {
+              mojo.define(name, deps, (...modules) => {
+                let result = factory(...modules);
+                resolve(result);
+                return result;

[Sami, 2016/06/20 16:58:16]

Did you mention this return could be removed?

[alex clarke (OOO till 29th), 2016/06/20 23:19:13]

We need the return but the resolve isn't needed.

+              });
+            });
+            moduleCache.set(name, promise);
+          }
+          return promise;
+        }
+      })();
+
+      // This code is run before the browser has sent us the mojo bindings so
+      // we need to get fancy and use nested proxy classes to define a promise
+      // to an arbitary window.mojo.services.myModule.myInterface.
+      if (window.hasOwnProperty("mojo")) {
+        let mojoBindings = new Map();
+        let resolvePending = true;
+
+        // Factory for returning the second level dynamic property which
+        // resolves to a promise to the corresponding mojo inteerface..

[Sami, 2016/06/20 16:58:16]

typo: interface.

[alex clarke (OOO till 29th), 2016/06/20 23:19:13]

Done.

[alex clarke (OOO till 29th), 2016/06/20 23:19:13]

Done.

+        let interfaceProxyFactory = function(serviceName) {
+          return new Proxy({}, {
+            get: function(target, interfaceName) {
+              let name = serviceName + "::" + interfaceName;
+              let binding = mojoBindings.get(name);
+              if (binding === undefined) {
+                binding = {};
+                binding.promise = new Promise(function(resolve, reject) {
+                  binding.resolve = resolve;
+                  binding.reject = reject;
+                  if (!resolvePending)
+                    reject();
+                });
+                mojoBindings.set(name, binding);
+              }
+              return binding.promise;
+            },
+            set: function(target, name, value) {
+              return false;

[Sami, 2016/06/20 16:58:16]

Should we throw an Error here?

[alex clarke (OOO till 29th), 2016/06/21 09:16:45]

Done.

+            }
+          });
+        };
+
+        // Top level dynamic property.
+        window.mojo.services = new Proxy({}, {
+          get: function(target, serviceName) {
+            if (!(serviceName in target)) {
+              let interfaceProxy = interfaceProxyFactory(serviceName);
+              target[serviceName] = interfaceProxy;
+              return interfaceProxy;
+            }
+            return target[serviceName];
+          },
+          set: function(target, name, value) {
+            return false;

[Sami, 2016/06/20 16:58:16]

Ditto.

[alex clarke (OOO till 29th), 2016/06/21 09:16:45]

Done.

+          }
+        });
+
+        // Resolve promises for the listed |serviceNames|.
+        window.mojo.resolvePromisesForServices = function(serviceNames) {

[Sami, 2016/06/20 16:58:16]

Should we call this resolvePromisesForServices_ since it's really an internal
function?

[alex clarke (OOO till 29th), 2016/06/20 23:19:13]

Done.

+          let numServices = serviceNames.length;
+          for (let i = 0; i < numServices; ++i) {
+            let serviceName = serviceNames[i];
+            // Use mojo to obtain the module binding.
+            define([
+                serviceName,
+                "mojo/public/js/core",
+                "mojo/public/js/router",
+                "content/public/renderer/frame_service_registry",
+                ], function(serviceMojom, mojoCore, routerModule,
+                            serviceProvider) {
+              // A mojom binding may contain bindings for a number of
+              // interfaces. Iterate through all of them and resolve any
+              // promises.
+              for (var m in serviceMojom) {

[Sami, 2016/06/20 16:58:16]

s/var/let/

Also maybe "for..of" would be more appropriate?

[alex clarke (OOO till 29th), 2016/06/20 23:19:13]

Done.

[alex clarke (OOO till 29th), 2016/06/20 23:19:13]

Done.

[Sami, 2016/06/21 10:22:26]

(Did you mean to leave the "in" here? Sometimes it can give surprising results
but maybe that's not an issue here)

[alex clarke (OOO till 29th), 2016/06/21 10:38:37]

for..of only works for iterables but serviceMojom is an object so we have to use
for..in here.

+                if (typeof serviceMojom[m] == "object") {
+                  let service = serviceMojom[m];
+                  let binding = mojoBindings.get(service.name);
+                  let interface = new service.proxyClass(
+                      new routerModule.Router(
+                          serviceProvider.connectToService(service.name)));
+                  if (binding === undefined) {
+                    // Store resolved promise in case binding is requested.
+                    mojoBindings.set(
+                        service.name, {"promise": Promise.resolve(interface)});
+                  } else {
+                    binding.resolve(interface);
+                    // Since this promise has been resolved we don't want to try
+                    // and reject it below!
+                    delete binding.reject;
+                  }
+                }
+              }
+            });
+          }
+          // Reject any remaining promises that didn't get resolved.
+          for (let [key, value] of mojoBindings) {
+            if ("reject" in value) {
+              value.reject();
+            }
+          }
+          // Reject any subsequent unknown properties.
+          resolvePending = false;
+        };
+      } )"));
+}
+
 }  // namespace headless