Mojom parser: Compute and validate struct field ordinals.

mojom/mojom_parser/parser/comment_merger_test.go

 package parser
 
 import (
         "mojom/mojom_parser/lexer"
         "mojom/mojom_parser/mojom"
         "testing"
 )
 
 func TestAttachComments(t *testing.T) {
         checkEq := func(expected, actual interface{}) {
@@ skipping 48 matching lines @@
 
         interfaceFoo := mojomFile.DeclaredObjects[0].(*mojom.MojomInterface)
         // Sanity-check that we got the right object.
         checkEq("InterfaceFoo", interfaceFoo.SimpleName())
         checkEq("// FinalInterfaceComment", interfaceFoo.AttachedComments().Final[0].Text)
 
         method1 := interfaceFoo.MethodsByOrdinal[0]
         // Sanity-check that we got the right method.
         checkEq("Method1", method1.SimpleName())
 
-        inParam1 := method1.Parameters.Fields[0]
+        inParam1 := method1.Parameters.FieldsInLexicalOrder[0]
         // Sanity-check that we got the right field.
         checkEq("in_param1", inParam1.SimpleName())
 
         checkEq("// Method1RightComment", method1.AttachedComments().Right[0].Text)
         checkEq("/* InParam1Comment */", inParam1.AttachedComments().Right[0].Text)
 
         checkEq(lexer.EmptyLine, mojomFile.FinalComments[0].Kind)
         checkEq("// FinalComments", mojomFile.FinalComments[1].Text)
 }
 
@@ skipping 32 matching lines @@
                         `
         descriptor := mojom.NewMojomDescriptor()
         parser := MakeParser("TestOnlyComments", "TestOnlyComments", source, descriptor, nil)
         parser.Parse()
 
         mojomFile := parser.GetMojomFile()
         comments := parser.GetComments()
 
         mojom.AttachCommentsToMojomFile(mojomFile, comments)
 }