Adds ConversationStarter class and stubs in Fetch API.

Follow up CLs will wire the fetch API up to a loader as well as invoke
the fetch API from AssistantSuggestionsController at the appropriate
points in the Assistant lifecycle.

Bug: b:148239201
Change-Id: I8eb816aab3eff180b90d4eb21371d81b6219ce0c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2018443
Commit-Queue: David Black <dmblack@google.com>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#735157}

ash/public/cpp/BUILD.gn

@@ -71,6 +71,8 @@ component("cpp") {
     "assistant/assistant_web_view_2.h",
     "assistant/assistant_web_view_factory.cc",
     "assistant/assistant_web_view_factory.h",
+    "assistant/conversation_starter.cc",
+    "assistant/conversation_starter.h",
     "assistant/conversation_starters_client.cc",
     "assistant/conversation_starters_client.h",
     "assistant/proactive_suggestions.cc",

ash/public/cpp/assistant/conversation_starter.cc

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ash/public/cpp/assistant/conversation_starter.h"
+
+namespace ash {
+
+ConversationStarter::ConversationStarter(const std::string& label,
+                                         const base::Optional<GURL>& action_url,
+                                         const base::Optional<GURL>& icon_url,
+                                         uint32_t required_permissions)
+    : label_(label),
+      action_url_(action_url),
+      icon_url_(icon_url),
+      required_permissions_(required_permissions) {}
+
+ConversationStarter::~ConversationStarter() = default;
+
+}  // namespace ash

ash/public/cpp/assistant/conversation_starter.h

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef ASH_PUBLIC_CPP_ASSISTANT_CONVERSATION_STARTER_H_
+#define ASH_PUBLIC_CPP_ASSISTANT_CONVERSATION_STARTER_H_
+
+#include <string>
+
+#include "ash/public/cpp/ash_public_export.h"
+#include "base/optional.h"
+#include "url/gurl.h"
+
+namespace ash {
+
+// Models an immutable conversation starter.
+class ASH_PUBLIC_EXPORT ConversationStarter {
+ public:
+  // Enumeration of possible permissions which a conversation starter may
+  // require in order to be presented to the user.
+  enum class Permission : uint32_t { kRelatedInfo = 1u };
+
+  ConversationStarter(const std::string& label,
+                      const base::Optional<GURL>& action_url,
+                      const base::Optional<GURL>& icon_url,
+                      uint32_t required_permissions);
+  ConversationStarter(const ConversationStarter& copy) = delete;
+  ConversationStarter& operator=(ConversationStarter& assign) = delete;
+  ~ConversationStarter();
+
+  const std::string& label() const { return label_; }
+  const base::Optional<GURL>& action_url() const { return action_url_; }
+  const base::Optional<GURL>& icon_url() const { return icon_url_; }
+  const uint32_t& required_permissions() const { return required_permissions_; }
+
+ private:
+  const std::string label_;
+  const base::Optional<GURL> action_url_;
+  const base::Optional<GURL> icon_url_;
+  const uint32_t required_permissions_;
+};
+
+}  // namespace ash
+
+#endif  // ASH_PUBLIC_CPP_ASSISTANT_CONVERSATION_STARTER_H_

ash/public/cpp/assistant/conversation_starters_client.h

@@ -5,16 +5,26 @@
 #ifndef ASH_PUBLIC_CPP_ASSISTANT_CONVERSATION_STARTERS_CLIENT_H_
 #define ASH_PUBLIC_CPP_ASSISTANT_CONVERSATION_STARTERS_CLIENT_H_
 
+#include <vector>
+
 #include "ash/public/cpp/ash_public_export.h"
+#include "base/callback_forward.h"
 
 namespace ash {
 
+class ConversationStarter;
+
 // The interface for the conversation starters feature browser client.
 class ASH_PUBLIC_EXPORT ConversationStartersClient {
  public:
   // Returns the singleton instance.
   static ConversationStartersClient* Get();
 
+  // Fetches conversation starters from the server, running |callback| with the
+  // returned list upon completion. Note that the returned list may be empty.
+  using Callback = base::OnceCallback<void(std::vector<ConversationStarter>&&)>;
+  virtual void FetchConversationStarters(Callback callback) = 0;
+
  protected:
   ConversationStartersClient();
   virtual ~ConversationStartersClient();

chrome/browser/ui/ash/assistant/conversation_starters_client_impl.cc

@@ -4,6 +4,9 @@
 
 #include "chrome/browser/ui/ash/assistant/conversation_starters_client_impl.h"
 
+#include <vector>
+
+#include "ash/public/cpp/assistant/conversation_starter.h"
 #include "chrome/browser/profiles/profile.h"
 
 ConversationStartersClientImpl::ConversationStartersClientImpl(Profile* profile)
@@ -12,3 +15,9 @@ ConversationStartersClientImpl::ConversationStartersClientImpl(Profile* profile)
 }
 
 ConversationStartersClientImpl::~ConversationStartersClientImpl() = default;
+
+// TODO(dmblack): Fetch conversation starters from the server.
+void ConversationStartersClientImpl::FetchConversationStarters(
+    Callback callback) {
+  std::move(callback).Run(std::vector<ash::ConversationStarter>());
+}

chrome/browser/ui/ash/assistant/conversation_starters_client_impl.h

@@ -18,6 +18,9 @@ class ConversationStartersClientImpl : public ash::ConversationStartersClient {
       ConversationStartersClientImpl& assign) = delete;
   ~ConversationStartersClientImpl() override;
 
+  // ash::ConversationStartersClient:
+  void FetchConversationStarters(Callback callback) override;
+
  private:
   Profile* const profile_;
 };