CroppingWindowCapturer::CreateCapturer() function to replace raw pointer version

The old CroppingWindowCapturer::Create() function returns a raw pointer, which
cannot explain the ownership.
So this change adds a CreateCapturer() function to return a unique_ptr.

BUG=webrtc:6513

Review-Url: https://codereview.webrtc.org/2496993003
Cr-Commit-Position: refs/heads/master@{#15045}

webrtc/modules/desktop_capture/cropping_window_capturer.cc

@@ -106,6 +106,12 @@ DesktopCapturer* CroppingWindowCapturer::Create(
     const DesktopCaptureOptions& options) {
   return DesktopCapturer::CreateWindowCapturer(options).release();
 }
+
+// static
+std::unique_ptr<DesktopCapturer> CroppingWindowCapturer::CreateCapturer(
+    const DesktopCaptureOptions& options) {
+  return DesktopCapturer::CreateWindowCapturer(options);
+}
 #endif
 
 }  // namespace webrtc

webrtc/modules/desktop_capture/cropping_window_capturer.h

@@ -24,7 +24,11 @@ namespace webrtc {
 class CroppingWindowCapturer : public DesktopCapturer,
                                public DesktopCapturer::Callback {
  public:
+  // Deprecated, use CreateCapturer()
   static DesktopCapturer* Create(const DesktopCaptureOptions& options);
+  static std::unique_ptr<DesktopCapturer> CreateCapturer(
+      const DesktopCaptureOptions& options);
+
   ~CroppingWindowCapturer() override;
 
   // DesktopCapturer implementation.

webrtc/modules/desktop_capture/cropping_window_capturer_win.cc

@@ -215,4 +215,11 @@ DesktopCapturer* CroppingWindowCapturer::Create(
   return new CroppingWindowCapturerWin(options);
 }
 
+// static
+std::unique_ptr<DesktopCapturer> CroppingWindowCapturer::CreateCapturer(
+    const DesktopCaptureOptions& options) {
+  return std::unique_ptr<DesktopCapturer>(
+      new CroppingWindowCapturerWin(options));
+}
+
 }  // namespace webrtc