GN: Change rtc_source_set targets --> rtc_static_library

webrtc/modules/desktop_capture/BUILD.gn

Index: webrtc/modules/desktop_capture/BUILD.gn
diff --git a/webrtc/modules/desktop_capture/BUILD.gn b/webrtc/modules/desktop_capture/BUILD.gn
index 8887ba99c3ecc5c146b5ea6d452a221d0e9da40c..46a768aac5e869ed35fd68d56950090eab48b255 100644
--- a/webrtc/modules/desktop_capture/BUILD.gn
+++ b/webrtc/modules/desktop_capture/BUILD.gn
@@ -12,7 +12,7 @@ import("../../build/webrtc.gni")
 use_desktop_capture_differ_sse2 =
     !is_ios && (current_cpu == "x86" || current_cpu == "x64")
 
-rtc_source_set("primitives") {
+rtc_static_library("primitives") {
   sources = [
     "desktop_capture_types.h",
     "desktop_frame.cc",
@@ -24,7 +24,7 @@ rtc_source_set("primitives") {
   ]
 }
 
-rtc_source_set("desktop_capture") {
+rtc_static_library("desktop_capture") {
   sources = [
     "cropped_desktop_frame.cc",
     "cropped_desktop_frame.h",
@@ -168,7 +168,7 @@ rtc_source_set("desktop_capture") {
 if (use_desktop_capture_differ_sse2) {
   # Have to be compiled as a separate target because it needs to be compiled
   # with SSE2 enabled.
-  rtc_source_set("desktop_capture_differ_sse2") {
+  rtc_static_library("desktop_capture_differ_sse2") {
     visibility = [ ":*" ]
     sources = [
       "differ_vector_sse2.cc",