Add a path for content/ to open and control a Bluetooth chooser dialog.

content/public/browser/bluetooth_chooser.h

+// Copyright 2015 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 CONTENT_PUBLIC_BROWSER_BLUETOOTH_CHOOSER_H_
+#define CONTENT_PUBLIC_BROWSER_BLUETOOTH_CHOOSER_H_
+
+#include <string>
+
+#include "base/strings/string16.h"
+#include "content/common/content_export.h"
+
+namespace content {
+
+// Represents a way to ask the user to select a Bluetooth device from a list of
+// options.
+class CONTENT_EXPORT BluetoothChooser {
+ public:
+  class Observer {
+   public:
+    // The user cancelled the chooser instead of selecting a device.
+    virtual void DialogCancelled(int chooser_id) = 0;
+    // The user selected device |device_id|.
+    virtual void DeviceSelected(int chooser_id,
+                                const std::string& device_id) = 0;
+
+    // As the dialog implementations grow more user-visible buttons and knobs,
+    // those knobs will cause new functions to be called here.

[jam, 2015/08/25 15:49:21]

are you certain that we will add more here? i.e. because if you're not sure, it
would be simpler (and more consistent with how we're trying to move the API to
use callbacks instead of single-method interfaces) to combine the two methods
above into one callback 

[Jeffrey Yasskin, 2015/08/25 17:13:13]

Yeah, we have at least "enable the adapter", "start scanning again", and "visit
the help url" in the mocks. Those are all no-argument functions, so we could
have a single callback that takes a big enum saying what happened, with one
optional device_id for the "Selected" option. Is that better?

[Jeffrey Yasskin, 2015/08/25 20:55:58]

Switched to a callback.

+
+   protected:
+    ~Observer() {}
+  };
+
+  // |observer| must outlive |this|. |chooser_id| is propagated to the Observer
+  // methods.
+  BluetoothChooser(Observer* observer, int chooser_id)
+      : observer_(observer), chooser_id_(chooser_id) {}
+  virtual ~BluetoothChooser();
+
+  // Lets the chooser tell the user the state of the Bluetooth adapter. This
+  // defaults to POWERED_ON.
+  enum class AdapterPresence { ABSENT, POWERED_OFF, POWERED_ON };
+  virtual void SetAdapterPresence(AdapterPresence presence) = 0;
+
+  // Lets the chooser tell the user whether discovery is happening. This
+  // defaults to DISCOVERING.
+  enum class DiscoveryState { FAILED_TO_START, DISCOVERING, IDLE };
+  virtual void ShowDiscoveryState(DiscoveryState state) = 0;
+
+  // Shows a new device in the chooser.
+  virtual void AddDevice(const std::string& device_id,
+                         const base::string16& device_name) = 0;
+  // Tells the chooser that a device is no longer available. The chooser should

[jam, 2015/08/25 15:49:21]

nit: blank line before

[Jeffrey Yasskin, 2015/08/25 17:13:13]

Done.

+  // not call DeviceSelected() for a device that's been removed.
+  virtual void RemoveDevice(const std::string& device_id) = 0;
+
+ protected:
+  // Subclasses call the observer methods through these wrappers, which add in
+  // the chooser ID.
+  void CallDialogCancelled() { observer_->DialogCancelled(chooser_id_); }

[jam, 2015/08/25 15:49:21]

this is against the content style guide:
https://www.chromium.org/developers/content-module/content-api

"content/public should contain only interfaces, structs and (rarely) static
functions"

if you used a callback here, you can bound the id to it

[Jeffrey Yasskin, 2015/08/25 17:13:14]

This seems in line with other interfaces in content/public that include a small
amount of behavior to make their implementations easier to use. e.g.
RenderViewObserver and WebContentsObserver. But I'm willing to move the logic to
subclasses anyway. Do the member variables need to move too?

I'll wait to do that until we decide whether to change the observer to a
callback.

[Jeffrey Yasskin, 2015/08/25 20:55:58]

Moot, now that there's a callback.

+  void CallDeviceSelected(const std::string& device_id) {
+    observer_->DeviceSelected(chooser_id_, device_id);
+  }
+
+ private:
+  Observer* const observer_;
+  const int chooser_id_;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_PUBLIC_BROWSER_BLUETOOTH_CHOOSER_H_