Have compositor_model_bench target near its source files.

gpu/tools/compositor_model_bench/BUILD.gn

+# Copyright 2015 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import("//build/config/ui.gni")
+
+if (is_linux && !is_chromeos && target_cpu != "arm" && use_x11) {
+  # GYP version: //gpu/tools/tools.gyp:compositor_model_bench
+  executable("compositor_model_bench") {
+    sources = [
+      "compositor_model_bench.cc",
+      "forward_render_model.cc",
+      "render_model_utils.cc",
+      "render_models.cc",
+      "render_tree.cc",
+      "shaders.cc",
+    ]
+
+    libs = [ "GL" ]
+
+    configs += [ "//build/config/linux:x11" ]
+
+    deps = [
+      "//base",
+      "//ui/gl",
+    ]
+  }
+}