GN: Change rtc_source_set targets --> rtc_static_library

webrtc/modules/desktop_capture/BUILD.gn

 # Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 import("//build/config/ui.gni")
 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",
     "desktop_frame.h",
     "desktop_geometry.cc",
     "desktop_geometry.h",
     "desktop_region.cc",
     "desktop_region.h",
   ]
 }
 
-rtc_source_set("desktop_capture") {
+rtc_static_library("desktop_capture") {
   sources = [
     "cropped_desktop_frame.cc",
     "cropped_desktop_frame.h",
     "cropping_window_capturer.cc",
     "cropping_window_capturer.h",
     "cropping_window_capturer_win.cc",
     "desktop_and_cursor_composer.cc",
     "desktop_and_cursor_composer.h",
     "desktop_capture_options.cc",
     "desktop_capture_options.h",
@@ skipping 123 matching lines @@
   ]
 
   if (use_desktop_capture_differ_sse2) {
     deps += [ ":desktop_capture_differ_sse2" ]
   }
 }
 
 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",
       "differ_vector_sse2.h",
     ]
 
     if (is_posix) {
       cflags = [ "-msse2" ]
     }
   }
 }