Mojo JS bindings: support auto-loading mojom.js deps.

mojo/public/js/new_bindings/base.js

Index: mojo/public/js/new_bindings/base.js
diff --git a/mojo/public/js/new_bindings/base.js b/mojo/public/js/new_bindings/base.js
index ef7aa32f73646c47bec8b51694b458ad50d929a7..db72d489db6ec016817ec1557a11812f33836b31 100644
--- a/mojo/public/js/new_bindings/base.js
+++ b/mojo/public/js/new_bindings/base.js
@@ -11,10 +11,53 @@ if (mojo && mojo.internal) {
 var mojo = mojo || {};
 mojo.internal = {};
 mojo.internal.global = this;
+mojo.config = {
+  // Whether to automatically load mojom dependencies.
+  // For example, if foo.mojom imports bar.mojom, |autoLoadMojomDeps| set to
+  // true means that loading foo.mojom.js will insert a <script> tag to load
+  // bar.mojom.js, if it hasn't been loaded.
+  //
+  // The URL of bar.mojom.js is determined by the relative path of bar.mojom
+  // (relative to the position of foo.mojom at build time) and the URL of
+  // foo.mojom.js. For exmple, if at build time the two mojom files are
+  // located at:
+  //   a/b/c/foo.mojom
+  //   a/b/d/bar.mojom
+  // and the URL of foo.mojom.js is:
+  //   http://example.org/scripts/b/c/foo.mojom.js
+  // then the URL of bar.mojom.js will be:
+  //   http://example.org/scripts/b/d/bar.mojom.js
+  //
+  // If you would like bar.mojom.js to live at a different location, you need
+  // to turn off |autoLoadMojomDeps| before loading foo.mojom.js, and manually
+  // load bar.mojom.js yourself. Similarly, you need to turn off the option if
+  // you merge bar.mojom.js and foo.mojom.js into a single file.
+  //
+  // Performance tip: Avoid loading the same mojom.js file multiple times.
+  // Assume that |autoLoadMojomDeps| is set to true:
+  // <!-- No duplicate loading; recommended. -->
+  // <script src="http://example.org/scripts/b/c/foo.mojom.js"></script>
+  //
+  // <!-- No duplicate loading, although unnecessary. -->
+  // <script src="http://example.org/scripts/b/d/bar.mojom.js"></script>
+  // <script src="http://example.org/scripts/b/c/foo.mojom.js"></script>
+  //
+  // <!-- Load bar.mojom.js twice; should be avoided. -->
+  // <script src="http://example.org/scripts/b/c/foo.mojom.js"></script>
+  // <script src="http://example.org/scripts/b/d/bar.mojom.js"></script>
+  autoLoadMojomDeps: true
+};
 
 (function() {
   var internal = mojo.internal;
 
+  var LoadState = {
+    PENDING_LOAD: 1,
+    LOADED: 2
+  };
+
+  var mojomRegistry = new Map();
+
   function exposeNamespace(namespace) {
     var current = internal.global;
     var parts = namespace.split('.');
@@ -29,5 +72,40 @@ mojo.internal.global = this;
     return current;
   }
 
+  function isMojomPendingLoad(id) {
+    return mojomRegistry.get(id) === LoadState.PENDING_LOAD;
+  }
+
+  function isMojomLoaded(id) {
+    return mojomRegistry.get(id) === LoadState.LOADED;
+  }
+
+  function markMojomPendingLoad(id) {
+    if (isMojomLoaded(id)) {
+      throw new Error('The following mojom file has been loaded: ' + id);
+    }
+
+    mojomRegistry.set(id, LoadState.PENDING_LOAD);
+  }
+
+  function markMojomLoaded(id) {
+    mojomRegistry.set(id, LoadState.LOADED);
+  }
+
+  function loadMojomIfNecessary(id, url) {
+    if (mojomRegistry.has(id)) {
+      return;
+    }
+
+    markMojomPendingLoad(id);
+    internal.global.document.write('<script type="text/javascript" src="' +
+                                   url + '"></script>');
+  }
+
   internal.exposeNamespace = exposeNamespace;
+  internal.isMojomPendingLoad = isMojomPendingLoad;
+  internal.isMojomLoaded = isMojomLoaded;
+  internal.markMojomPendingLoad = markMojomPendingLoad;
+  internal.markMojomLoaded = markMojomLoaded;
+  internal.loadMojomIfNecessary = loadMojomIfNecessary;
 })();