Add Jpeg frame writer for test support.

webrtc/test/BUILD.gn

Index: webrtc/test/BUILD.gn
diff --git a/webrtc/test/BUILD.gn b/webrtc/test/BUILD.gn
index 799642d1e197d224d40d42c30f590085e04ba67b..6ac511ead56ca10e42233058da7888b4a34bac3f 100644
--- a/webrtc/test/BUILD.gn
+++ b/webrtc/test/BUILD.gn
@@ -205,6 +205,7 @@ if (!build_with_chromium) {
       ":test_support",
       ":video_test_common",
       "..:webrtc_common",
+      "../api:video_frame_api",
       "../common_video",
       "../rtc_base:rtc_base_approved",
       "../system_wrappers",
@@ -213,6 +214,11 @@ if (!build_with_chromium) {
       "//third_party/gflags",
     ]
 
+    if (!is_ios) {
+      deps += [ "//third_party:jpeg" ]
+      sources += [ "testsupport/jpeg_frame_writer.cc" ]
+    }
+
     public_deps = [
       ":fileutils",
     ]