Unit tests have been created for the GPUTiming.

ui/gl/BUILD.gn

Index: ui/gl/BUILD.gn
diff --git a/ui/gl/BUILD.gn b/ui/gl/BUILD.gn
index 2dc61403817b40cee2d6e14276aaef5f8f6cc403..b2ac8fc357c4bc2c7b5759b5a34e53e42345efab 100644
--- a/ui/gl/BUILD.gn
+++ b/ui/gl/BUILD.gn
@@ -268,6 +268,8 @@ source_set("gl_unittest_utils") {
     "gl_mock.cc",
     "gl_mock.h",
     "gl_mock_autogen_gl.h",
+    "gpu_timing_fake.cc",
+    "gpu_timing_fake.h",
   ]
 
   configs += [ "//third_party/khronos:khronos_headers" ]
@@ -281,13 +283,16 @@ source_set("gl_unittest_utils") {
 test("gl_unittests") {
   sources = [
     "gl_api_unittest.cc",
+    "gpu_timing_unittest.cc",
     "test/run_all_unittests.cc",
   ]
 
   deps = [
     ":gl",
+    ":gl_unittest_utils",
     "//base",
     "//base/test:test_support",
+    "//testing/gmock",
     "//testing/gtest",
   ]
 }