Refactor fileutils.cc/h and fileutils_unittests.cc into their own targets.

webrtc/test/BUILD.gn

Index: webrtc/test/BUILD.gn
diff --git a/webrtc/test/BUILD.gn b/webrtc/test/BUILD.gn
index 1b3c05973ac7c1a17ee9e69c389e4b43893afbcb..a88274361d1d73bee6328f12444b6f2dffa04203 100644
--- a/webrtc/test/BUILD.gn
+++ b/webrtc/test/BUILD.gn
@@ -104,14 +104,20 @@ rtc_source_set("test_main") {
   ]
 }
 
+rtc_source_set("fileutils") {
+  testonly = true
+  sources = [
+    "testsupport/fileutils.cc",
+    "testsupport/fileutils.h",
+  ]
+}
+
 rtc_source_set("test_support") {
   testonly = true
 
   sources = [
     "gmock.h",
     "gtest.h",
-    "testsupport/fileutils.cc",
-    "testsupport/fileutils.h",
     "testsupport/frame_reader.cc",
     "testsupport/frame_reader.h",
     "testsupport/frame_writer.cc",
@@ -130,6 +136,7 @@ rtc_source_set("test_support") {
   ]
 
   deps = [
+    ":fileutils",
     ":video_test_common",
     "../base:gtest_prod",
     "../base:rtc_base_approved",
@@ -204,7 +211,6 @@ rtc_test("test_support_unittests") {
     "rtp_file_reader_unittest.cc",
     "rtp_file_writer_unittest.cc",
     "testsupport/always_passing_unittest.cc",
-    "testsupport/fileutils_unittest.cc",
     "testsupport/frame_reader_unittest.cc",
     "testsupport/frame_writer_unittest.cc",
     "testsupport/metrics/video_metrics_unittest.cc",
@@ -236,6 +242,7 @@ rtc_test("test_support_unittests") {
   }
 
   deps += [
+    ":fileutils_unittests",
     ":test_common",
     ":test_main",
     "../modules/video_capture",
@@ -243,6 +250,17 @@ rtc_test("test_support_unittests") {
     "//testing/gtest",
   ]
 }
+rtc_source_set("fileutils_unittests") {
+  testonly = true
+  sources = [
+    "testsupport/fileutils_unittest.cc",
+  ]
+  deps = [
+    ":fileutils",
+    "//testing/gmock",
+    "//testing/gtest",
+  ]
+}
 
 rtc_source_set("test_common") {
   testonly = true