Make RenderPass::Id an isolated class

cc/surfaces/surface_aggregator_test_helpers.h

Index: cc/surfaces/surface_aggregator_test_helpers.h
diff --git a/cc/surfaces/surface_aggregator_test_helpers.h b/cc/surfaces/surface_aggregator_test_helpers.h
index 75bfaeb10ae839c5240008f08771c3f8741ee140..e8440e6bcc2a256ee34fb104f378b0d0bf52a7e7 100644
--- a/cc/surfaces/surface_aggregator_test_helpers.h
+++ b/cc/surfaces/surface_aggregator_test_helpers.h
@@ -33,7 +33,7 @@ struct Quad {
     return quad;
   }
 
-  static Quad RenderPassQuad(RenderPass::Id id) {
+  static Quad RenderPassQuad(RenderPassId id) {
     Quad quad;
     quad.material = DrawQuad::RENDER_PASS;
     quad.render_pass_id = id;
@@ -46,7 +46,7 @@ struct Quad {
   // Set when material==DrawQuad::SOLID_COLOR.
   SkColor color;
   // Set when material==DrawQuad::RENDER_PASS.
-  RenderPass::Id render_pass_id;
+  RenderPassId render_pass_id;
 
  private:
   Quad()
@@ -56,14 +56,14 @@ struct Quad {
 };
 
 struct Pass {
-  Pass(Quad* quads, size_t quad_count, RenderPass::Id id)
+  Pass(Quad* quads, size_t quad_count, RenderPassId id)
       : quads(quads), quad_count(quad_count), id(id) {}
   Pass(Quad* quads, size_t quad_count)
       : quads(quads), quad_count(quad_count), id(1, 1) {}
 
   Quad* quads;
   size_t quad_count;
-  RenderPass::Id id;
+  RenderPassId id;
 };
 
 void AddSurfaceQuad(TestRenderPass* pass,