Mojo JS bindings: add support to generate "dual-mode" code.

mojo/public/tools/bindings/mojom.gni

 # Copyright 2014 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.
 
 declare_args() {
   # Indicates whether typemapping should be supported in this build
   # configuration. This may be disabled when building external projects which
   # depend on //mojo but which do not need/want all of the Chromium tree
   # dependencies that come with typemapping.
   #
@@ skipping 140 matching lines @@
 #   cpp_only (optional)
 #       If set to true, only the C++ bindings targets will be generated.
 #
 #   use_new_js_bindings (optional)
 #       If set to true, the generated JS code will use the new module loading
 #       approach and the core API exposed by Web IDL.
 #       Default value is true.
 #       TODO(yzshen): Convert all users to use new JS bindings and remove the
 #       old mode.
 #
+#   js_bindings_mode (optional)
+#       |js_bindings_mode| and |use_new_js_bindings| are mutually exclusive. You
+#       can only specify at most one of them.
+#       - "new" (default): generate only the new-style JS bindings;
+#       - "both": generate both the old- and new-style JS bindings;
+#       - "old": generate only the old-style JS bindings.
+#       TODO(yzshen): Convert all users to use new JS bindings and remove the
+#       old mode.
+#
 #   component_output_prefix (optional)
 #       The prefix to use for the output_name of any component library emitted
 #       for generated C++ bindings. If this is omitted, C++ bindings targets are
 #       emitted as source_sets instead. Because this controls the name of the
 #       output shared library binary in the root output directory, it must be
 #       unique across the entire build configuration.
 #
 #       This is required if |component_macro_prefix| is specified.
 #
 #   component_macro_prefix (optional)
@@ skipping 34 matching lines @@
 #   component_deps (optional)
 #       The list of component deps to add to replace overridden_deps.
 #   overridden_deps_blink (optional)
 #   component_deps_blink (optional)
 #       These two parameters are the blink variants of the previous two.
 template("mojom") {
   assert(
       defined(invoker.sources) || defined(invoker.deps) ||
           defined(invoker.public_deps),
       "\"sources\" or \"deps\" must be defined for the $target_name template.")
+
+  assert(
+      !defined(invoker.use_new_js_bindings) ||
+          !defined(invoker.js_bindings_mode),
+      "You shouldn't specify both \"use_new_js_bindings\" and " +
+      "\"js_bindings_mode\".")
+
   if (defined(invoker.export_class_attribute) ||
       defined(invoker.export_define) || defined(invoker.export_header)) {
     assert(defined(invoker.export_class_attribute))
     assert(defined(invoker.export_define))
     assert(defined(invoker.export_header))
     assert(!defined(invoker.component_macro_prefix))
   }
   if (defined(invoker.export_class_attribute_blink) ||
       defined(invoker.export_define_blink) ||
       defined(invoker.export_header_blink)) {
     assert(defined(invoker.export_class_attribute_blink))
     assert(defined(invoker.export_define_blink))
     assert(defined(invoker.export_header_blink))
     assert(!defined(invoker.component_macro_prefix))
   }
   if (defined(invoker.overridden_deps) || defined(invoker.component_deps)) {
     assert(defined(invoker.overridden_deps))
     assert(defined(invoker.component_deps))
   }
 
   if (defined(invoker.overridden_deps_blink) ||
       defined(invoker.component_deps_blink)) {
     assert(defined(invoker.overridden_deps_blink))
     assert(defined(invoker.component_deps_blink))
   }
 
-  if (defined(invoker.use_new_js_bindings)) {
-    assert(invoker.use_new_js_bindings || !invoker.use_new_js_bindings,
-           "Surpress unused variable error when JS bindings are not needed.")
+  js_bindings_mode = "new"
+  if (defined(invoker.js_bindings_mode)) {
+    js_bindings_mode = invoker.js_bindings_mode
   }
+  if (defined(invoker.use_new_js_bindings) && !invoker.use_new_js_bindings) {
+    js_bindings_mode = "old"
+  }
+  assert(js_bindings_mode == "new" || js_bindings_mode == "both" ||
+             js_bindings_mode == "old",
+         "Invalid js_bindings_mode value.")
 
   all_deps = []
   if (defined(invoker.deps)) {
     all_deps += invoker.deps
   }
   if (defined(invoker.public_deps)) {
     all_deps += invoker.public_deps
   }
 
   if (defined(invoker.component_macro_prefix)) {
@@ skipping 615 matching lines @@
         deps = [
           "//mojo/public/tools/bindings:precompile_templates",
         ]
         outputs = generator_js_outputs
         args = common_generator_args
         args += [
           "-g",
           "javascript",
         ]
 
-        if (!defined(invoker.use_new_js_bindings) ||
-            invoker.use_new_js_bindings) {
-          args += [ "--use_new_js_bindings" ]
-        }
+        args += [
+          "--js_bindings_mode",
+          js_bindings_mode,
+        ]
       }
     }
 
     js_target_name = target_name + "_js"
     group(js_target_name) {
       public_deps = []
       if (defined(invoker.sources)) {
         public_deps += [ ":$generator_js_target_name" ]
       }
 
@@ skipping 32 matching lines @@
     forward_variables_from(invoker,
                            "*",
                            [
                              "output_prefix",
                              "macro_prefix",
                            ])
     component_output_prefix = invoker.output_prefix
     component_macro_prefix = invoker.macro_prefix
   }
 }