Add DesktopFrame rotation functions

webrtc/modules/desktop_capture/rgba_color.h

Index: webrtc/modules/desktop_capture/rgba_color.h
diff --git a/webrtc/modules/desktop_capture/rgba_color.h b/webrtc/modules/desktop_capture/rgba_color.h
index 1236d03ee67c21c0c13d4c3802a5936ed97ae13a..c5b6b8d60bd790873813702b7e6daa61cb85349f 100644
--- a/webrtc/modules/desktop_capture/rgba_color.h
+++ b/webrtc/modules/desktop_capture/rgba_color.h
@@ -40,6 +40,10 @@ struct RgbaColor final {
   // instance from the ToUInt32() result of another RgbaColor instance.
   explicit RgbaColor(uint32_t bgra);
 
+  // Converts an int to uint32_t, and creates a RGBA instance. This constructor
+  // helps users to write RgbaColor(0) without ambiguous conversion error.
+  explicit RgbaColor(int bgra);
+
   // Returns true if |this| and |right| is the same color.
   bool operator==(const RgbaColor& right) const;