remove increment flag on imageContexts.new()

Rename the methods to match my understanding of the behaviour.

Signed-off-by: Daniel Nephin <dnephin@docker.com>

builder/dockerfile/dispatchers.go

@@ -189,7 +189,7 @@ func from(b *Builder, args []string, attributes map[string]bool, original string
 		return err
 	}
 	b.resetImageCache()
-	if _, err := b.imageContexts.new(ctxName, true); err != nil {
+	if _, err := b.imageContexts.add(ctxName); err != nil {
 		return err
 	}
 
@@ -846,11 +846,7 @@ func mountByRef(b *Builder, name string) (*imageMount, error) {
 	if err != nil {
 		return nil, err
 	}
-	im, err := b.imageContexts.new("", false)
-	if err != nil {
-		return nil, err
-	}
-	im.id = image.ImageID()
+	im := b.imageContexts.newImageMount(image.ImageID())
 	return im, nil
 }
 

builder/dockerfile/imagecontext.go

@@ -22,7 +22,11 @@ type imageContexts struct {
 	currentName string
 }
 
-func (ic *imageContexts) new(name string, increment bool) (*imageMount, error) {
+func (ic *imageContexts) newImageMount(id string) *imageMount {
+	return &imageMount{ic: ic, id: id}
+}
+
+func (ic *imageContexts) add(name string) (*imageMount, error) {
 	im := &imageMount{ic: ic}
 	if len(name) > 0 {
 		if ic.byName == nil {
@@ -33,10 +37,8 @@ func (ic *imageContexts) new(name string, increment bool) (*imageMount, error) {
 		}
 		ic.byName[name] = im
 	}
-	if increment {
-		ic.list = append(ic.list, im)
-	}
 	ic.currentName = name
+	ic.list = append(ic.list, im)
 	return im, nil
 }