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..94471186f19d59ed32dd5f6e232692c98a808028 100644
--- a/webrtc/modules/desktop_capture/rgba_color.h
+++ b/webrtc/modules/desktop_capture/rgba_color.h
@@ -13,8 +13,6 @@
 
 #include <stdint.h>
 
-#include "webrtc/modules/desktop_capture/desktop_frame.h"
-
 namespace webrtc {
 
 // A four-byte structure to store a color in BGRA format. This structure also
@@ -40,6 +38,10 @@ 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;
 
@@ -53,9 +55,6 @@ struct RgbaColor final {
   uint8_t red;
   uint8_t alpha;
 };
-static_assert(
-    DesktopFrame::kBytesPerPixel == sizeof(RgbaColor),
-    "A pixel in DesktopFrame should be safe to be represented by a RgbaColor");
 
 }  // namespace webrtc