Make RenderPass::Id an isolated class

cc/trees/layer_tree_host_unittest_copyrequest.cc

Index: cc/trees/layer_tree_host_unittest_copyrequest.cc
diff --git a/cc/trees/layer_tree_host_unittest_copyrequest.cc b/cc/trees/layer_tree_host_unittest_copyrequest.cc
index 12fc63128f060cae65b923a4a6ce081728da9a4b..89a267a1ec6c9c94305de2f0d19a40433a73e24a 100644
--- a/cc/trees/layer_tree_host_unittest_copyrequest.cc
+++ b/cc/trees/layer_tree_host_unittest_copyrequest.cc
@@ -388,12 +388,12 @@ class LayerTreeHostTestHiddenSurfaceNotAllocatedForSubtreeCopyRequest
     // |parent| owns a surface, but it was hidden and not part of the copy
     // request so it should not allocate any resource.
     EXPECT_FALSE(renderer->HasAllocatedResourcesForTesting(
-        parent->render_surface()->RenderPassId()));
+        parent->render_surface()->GetRenderPassId()));
 
     // |copy_layer| should have been rendered to a texture since it was needed
     // for a copy request.
     EXPECT_TRUE(renderer->HasAllocatedResourcesForTesting(
-        copy_layer->render_surface()->RenderPassId()));
+        copy_layer->render_surface()->GetRenderPassId()));
 
     did_draw_ = true;
   }