[discover] Add DiscoverManager and ModuleOutput FIDL protocols

MI4-2399 #done

TESTED=build

Change-Id: I349581101aa35e29e14dee3058b62bcde963cbd9

sdk/fidl/fuchsia.app.discover/BUILD.gn

+# Copyright 2019 The Fuchsia Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import("//build/fidl/fidl.gni")
+
+fidl("fuchsia.app.discover") {
+  sdk_category = "partner"
+
+  sources = [
+    "discover_manager.fidl",
+    "module_output.fidl",
+  ]
+
+  deps = [
+    "//sdk/fidl/fuchsia.app",
+  ]
+}

sdk/fidl/fuchsia.app.discover/OWNERS

+miguelfrde@google.com
+schilit@google.com

sdk/fidl/fuchsia.app.discover/README.md

+# Discover FIDL API
+
+Experimental.
+
+## DiscoverManager
+
+Sessionmgr routes modules' requests for ModuleOutputWriter to discovermgr via
+the DiscoverRegistry protocol. While doing so, it provides the discovermgr with
+a unique identifier for the module.
+
+This interface is meant to be used only by sessionmgr.
+
+## ModuleOutputWriter
+
+Provided to modules to write to output parameters. Entities written to these outputs
+will be used in suggested action inputs by the discovermgr.
+
+This interface is meant to be used by modules.

sdk/fidl/fuchsia.app.discover/discover_manager.fidl

+// Copyright 2019 The Fuchsia Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+library fuchsia.app.discover;
+
+using fuchsia.app;
+
+/// Interface between sessionmgr and discovermgr to route service connections
+/// requests that require module scoping.
+[Discoverable]
+protocol DiscoverRegistry {
+    /// Retrieves a module output writer for the module identified by |module|.
+    RegisterModuleOutputWriter(ModuleIdentifier module, request<ModuleOutputWriter> request);
+};
+
+table ModuleIdentifier {
+    /// The ID of the story to which the module belongs.
+    1: fuchsia.app.StoryId story_id;
+
+    /// The named path leading up to this module instance. This path is a unique
+    /// identifier of the module in the story.
+    2: vector<string> module_path;
+};

sdk/fidl/fuchsia.app.discover/module_output.fidl

+// Copyright 2019 The Fuchsia Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+library fuchsia.app.discover;
+
+[Discoverable]
+protocol ModuleOutputWriter {
+    /// Writes the |entity_reference| to the module's |output_parameter_name|
+    /// output. If no entity is provided, the output will be unset.
+    /// Return happens upon completion of a successful write.
+    Write(string output_name, string? entity_reference) -> () error OutputError;
+};
+
+/// Errors that can occur when writing to an output.
+enum OutputError : int32 {
+    /// If the output doesn't match a parameter defined in the module manifest
+    /// for the action currently being handled by the module.
+    UNKNOWN_NAME = 1;
+
+    /// If the entity reference couldn't be resolved.
+    UNKNOWN_ENTITY_REFERENCE = 2;
+
+    /// If the entity type written doesn't match the type defined in the module
+    /// manifest for the action currently being handled by the module..
+    INVALID_ENTITY_TYPE = 3;
+};