media/gpu/test: Minor cleanup in video decoder test build file.

This CL removes a dependency from the video decoder test environment
build target that was mostly unused. Only video.h/cc are used, which
are moved to the test helpers target so they can also be reused by the
upcoming the video encoder tests.

TEST=Built video_decode_accelerator_tests target

BUG=None

Change-Id: I2aa6590ceaca9af423a3ff0ba5bda0a4fae8b2b4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2087492Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Commit-Queue: David Staessens <dstaessens@chromium.org>
Cr-Commit-Position: refs/heads/master@{#747138}

media/gpu/BUILD.gn

@@ -538,6 +538,7 @@ if (use_v4l2_codec || use_vaapi) {
     data = [ "//media/test/data/" ]
     deps = [
       ":buildflags",
+      "test:helpers",
       "test:video_player",
       "test:video_player_test_environment",
       "//media:test_support",

media/gpu/test/BUILD.gn

@@ -12,6 +12,8 @@ source_set("helpers") {
     "image.h",
     "image_quality_metrics.cc",
     "image_quality_metrics.h",
+    "video.cc",
+    "video.h",
     "video_frame_helpers.cc",
     "video_frame_helpers.h",
     "video_test_environment.cc",
@@ -99,8 +101,6 @@ static_library("video_player_thumbnail_renderer") {
 static_library("video_player") {
   testonly = true
   sources = [
-    "video.cc",
-    "video.h",
     "video_player/frame_renderer.h",
     "video_player/frame_renderer_dummy.cc",
     "video_player/frame_renderer_dummy.h",
@@ -128,7 +128,6 @@ static_library("video_player_test_environment") {
   deps = [
     ":frame_file_writer",
     ":helpers",
-    ":video_player",
     "//media/gpu",
   ]
 }