add FieldByName to the interface of reflect.StructType

R=rsc
DELTA=34  (33 added, 0 deleted, 1 changed)
OCL=31752
CL=31754

src/pkg/reflect/all_test.go

diff --git a/src/pkg/reflect/all_test.go b/src/pkg/reflect/all_test.go
index 52e85f4..5a639fb 100644
--- a/src/pkg/reflect/all_test.go
+++ b/src/pkg/reflect/all_test.go
@@ -214,9 +214,18 @@
 	styp := etyp.(*StructType);
 	f := styp.Field(0);
 	testType(t, 5, f.Type, "chan *int32");
-	f = styp.Field(1);
+
+	f, present := styp.FieldByName("d");
+	if !present {
+		t.Errorf("FieldByName says present field is absent");
+	}
 	testType(t, 6, f.Type, "float32");
 
+	f, present = styp.FieldByName("absent");
+	if present {
+		t.Errorf("FieldByName says absent field is present");
+	}
+
 	typ = Typeof(([32]int32)(nil));
 	testType(t, 7, typ, "[32]int32");
 	testType(t, 8, typ.(*ArrayType).Elem(), "int32");

src/pkg/reflect/type.go

diff --git a/src/pkg/reflect/type.go b/src/pkg/reflect/type.go
index fe7619f..6a0b70a 100644
--- a/src/pkg/reflect/type.go
+++ b/src/pkg/reflect/type.go
@@ -455,6 +455,7 @@
 	Type Type;
 	Tag string;
 	Offset uintptr;
+	Index int;
 	Anonymous bool;
 }
 
@@ -482,6 +483,29 @@
 	return;
 }
 
+// FieldByName returns the field with the provided name and a boolean to indicate
+// that the field was found..
+func (t *StructType) FieldByName(name string) (f StructField, present bool) {
+	for i, p := range t.fields {
+		if p.name == nil || *p.name != name {
+			continue;
+		}
+		f.Name = *p.name;
+		f.Type = toType(*p.typ);
+		if p.pkgPath != nil {
+			f.PkgPath = *p.pkgPath;
+		}
+		if p.tag != nil {
+			f.Tag = *p.tag;
+		}
+		f.Offset = p.offset;
+		f.Index = i;
+		present = true;
+		break;
+	}
+	return;
+}
+
 // NumField returns the number of struct fields.
 func (t *StructType) NumField() int {
 	return len(t.fields);