Move VideoEncoderSoftwareFallbackWrapper from webrtc/video_encoder.h to webrtc/media/engine/

webrtc/media/BUILD.gn

Index: webrtc/media/BUILD.gn
diff --git a/webrtc/media/BUILD.gn b/webrtc/media/BUILD.gn
index efa81d499ef7a5e4619bad2ea6072889969eb530..c3c456c2977887c793537306f0c5f0a665d85111 100644
--- a/webrtc/media/BUILD.gn
+++ b/webrtc/media/BUILD.gn
@@ -86,6 +86,8 @@ rtc_static_library("rtc_media") {
     "engine/payload_type_mapper.h",
     "engine/simulcast.cc",
     "engine/simulcast.h",
+    "engine/videoencodersoftwarefallbackwrapper.cc",
+    "engine/videoencodersoftwarefallbackwrapper.h",
     "engine/webrtccommon.h",
     "engine/webrtcmediaengine.cc",
     "engine/webrtcmediaengine.h",
@@ -289,6 +291,7 @@ if (rtc_include_tests) {
       "engine/nullwebrtcvideoengine_unittest.cc",
       "engine/payload_type_mapper_unittest.cc",
       "engine/simulcast_unittest.cc",
+      "engine/videoencodersoftwarefallbackwrapper_unittest.cc",
       "engine/webrtcmediaengine_unittest.cc",
       "engine/webrtcvideocapturer_unittest.cc",
       "engine/webrtcvideoengine2_unittest.cc",