Mojo: Add support for constants to the IDL compiler.

mojo/public/interfaces/bindings/tests/sample_service.mojom

 // Copyright 2013 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.
 
 import "sample_import.mojom"
 import "sample_import2.mojom"
 
 [JavaPackage="org.chromium.mojo.bindings.test"]
 module sample {
 
+const uint8 kThree = 3;
+
 struct Bar {
   enum Type {
     TYPE_VERTICAL = 1 << 0,
     TYPE_HORIZONTAL = (1 << 1) + 0,
     TYPE_BOTH = TYPE_VERTICAL | TYPE_HORIZONTAL,
     TYPE_INVALID
   };
   uint8 alpha = (0x100 - 1) @0;
   uint8 beta @1;
   uint8 gamma @2;
   Type type = sample.Bar.TYPE_VERTICAL @3;
 };
 
 [RequiredFields=7]
 struct Foo {
-  string name = "Fooby" @8;
+  const string kFooby = "Fooby";
+  string name = kFooby @8;
   int32 x @0;
   int32 y @1;
   bool a = true @2;
   bool b @3;
   bool c @4;
   Bar bar @5;
   Bar[] extra_bars @7;
-  uint8[] data = [1,2,3] @6;
+  uint8[] data = [1,2,kThree] @6;
   handle<message_pipe> source @9;
   handle<data_pipe_consumer>[] input_streams @10;
   handle<data_pipe_producer>[] output_streams @11;
   bool[][] array_of_array_of_bools @12;
 };
 
 struct DefaultsTestInner {
   int32 age @2;
   string[] names = ["Jim"] @1;
   int32 height = 6*12 @3;
 };
 
 struct DefaultsTest {
   sample.DefaultsTestInner[] people = [{32, ["Bob", "Bobby"]}] @1;
   uint8[] data = [1, 2, 3] @2;
   imported.Point point = {7, 15} @3;
   int32[] shape_masks = [1 << imported.SHAPE_RECTANGLE] @4;
   imported.Thing thing = {imported.SHAPE_CIRCLE, imported.COLOR_BLACK};
   Bar.Type bar_type = Bar.TYPE_BOTH;
 };
 
 [Peer=ServiceClient]
 interface Service {
   enum BazOptions {
     BAZ_REGULAR = 0,
     BAZ_EXTRA
   };
+  const uint8 kFavoriteBaz = 1;
   Frobinate@0(Foo foo @0, BazOptions baz @1, Port port @2);
 };
 
 [Peer=Service]
 interface ServiceClient {
   DidFrobinate@0(int32 result @0);
 };
 
 // This interface is referenced above where it is defined. It also refers to
 // itself from a method.
 interface Port {
   PostMessage@0(string message_text @0, Port[] extra_ports@1);
 };
 
 }