[Video Capture, Linux] Make VideoCaptureDeviceFactoryLinux testable

Follow-up to https://chromium-review.googlesource.com/c/chromium/src/+/1120856

This CL is a pure refactoring and has no intended function change.

This CL is part of a series, see Design Doc at
https://docs.google.com/document/d/1ihGDZloUGdDpZ5XfmiI3AcqsSxOP9kOe5GxXOTqpHW4/edit?usp=sharing

Test: capture_unittests with physical camera attached
Bug: 768887
Change-Id: Ia9bb5c832066d43d3a2295e9a6c97a31ebc266ed
Reviewed-on: https://chromium-review.googlesource.com/1121239Reviewed-by: Emircan Uysaler <emircan@chromium.org>
Commit-Queue: Christian Fremerey <chfremer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574963}

media/capture/video/linux/video_capture_device_factory_linux.h

@@ -21,6 +21,14 @@ namespace media {
 class CAPTURE_EXPORT VideoCaptureDeviceFactoryLinux
     : public VideoCaptureDeviceFactory {
  public:
+  class CAPTURE_EXPORT DeviceProvider {
+   public:
+    virtual ~DeviceProvider() {}
+    virtual void GetDeviceIds(std::vector<std::string>* target_container) = 0;
+    virtual std::string GetDeviceModelId(const std::string& device_id) = 0;
+    virtual std::string GetDeviceDisplayName(const std::string& device_id) = 0;
+  };
+
   explicit VideoCaptureDeviceFactoryLinux(
       scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner);
   ~VideoCaptureDeviceFactoryLinux() override;
@@ -34,7 +42,17 @@ class CAPTURE_EXPORT VideoCaptureDeviceFactoryLinux
       VideoCaptureFormats* supported_formats) override;
 
  private:
+  bool HasUsableFormats(int fd, uint32_t capabilities);
+  std::list<float> GetFrameRateList(int fd,
+                                    uint32_t fourcc,
+                                    uint32_t width,
+                                    uint32_t height);
+  void GetSupportedFormatsForV4L2BufferType(
+      int fd,
+      VideoCaptureFormats* supported_formats);
+
   scoped_refptr<V4L2CaptureDevice> v4l2_;
+  std::unique_ptr<DeviceProvider> device_provider_;
   scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner_;
   DISALLOW_COPY_AND_ASSIGN(VideoCaptureDeviceFactoryLinux);
 };