[extension SW] Support lazy events from extension service workers.

extensions/browser/lazy_context_task_queue.h

+// Copyright 2017 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 EXTENSIONS_BROWSER_LAZY_CONTEXT_TASK_QUEUE_H_
+#define EXTENSIONS_BROWSER_LAZY_CONTEXT_TASK_QUEUE_H_
+
+#include "base/callback.h"
+#include "extensions/common/extension_id.h"
+#include "url/gurl.h"
+
+namespace content {
+class BrowserContext;
+class RenderProcessHost;
+}  // namespace content
+
+namespace extensions {
+class Extension;
+class LazyContextId;
+
+// Interface for performing tasks after loading lazy contexts of an extension.
+//
+// Lazy contexts are non-persistent, so they can unload any time and this
+// interface exposes an async mechanism to perform tasks after loading the
+// context.
+class LazyContextTaskQueue {
+ public:
+  // Represents information about an extension lazy context, which is passed to
+  // consumers that add tasks to LazyContextTaskQueue.
+  struct ContextInfo {
+    const ExtensionId extension_id;
+    content::RenderProcessHost* const render_process_host;
+    const int worker_thread_id;
+    const GURL url;
+    ContextInfo(const ExtensionId& extension_id,
+                content::RenderProcessHost* render_process_host,
+                int worker_thread_id,
+                const GURL& url)
+        : extension_id(extension_id),
+          render_process_host(render_process_host),
+          worker_thread_id(worker_thread_id),
+          url(url) {}
+  };
+  using PendingTask = base::Callback<void(std::unique_ptr<ContextInfo> params)>;
+
+  // Returns true if the task should be added to the queue (that is, if the
+  // extension has a lazy background page or service worker that isn't ready
+  // yet).
+  virtual bool ShouldEnqueueTask(content::BrowserContext* context,
+                                 const Extension* extension) = 0;
+
+  // Adds a task to the queue for a given extension. If this is the first
+  // task added for the extension, its "lazy context" (i.e. lazy background
+  // page for event pages, service worker for extension service workers) will
+  // be loaded. The task will be called either when the page is loaded,
+  // or when the page fails to load for some reason (e.g. a crash or browser
+  // shutdown). In the latter case, the ContextInfo will be nullptr.
+  //
+  // TODO(lazyboy): Remove "ToDispatchEvent" suffix and simply call this
+  // AddPendingTask. Issues:
+  // 1. We already have LazyBackgroundTaskQueue::AddPendingTask. Moreover, that
+  //    is heavily used thoughout the codebase.
+  // 2. LazyBackgroundTaskQueue::AddPendingTask is tied to ExtensionHost. This
+  //    class should be ExtensionHost agnostic.
+  virtual void AddPendingTaskToDispatchEvent(LazyContextId* context_id,
+                                             const PendingTask& task) = 0;
+};
+
+}  // namespace extensions
+
+#endif  // EXTENSIONS_BROWSER_LAZY_CONTEXT_TASK_QUEUE_H_