Add remaining trivial targets for the Linux GN build

tools/perf/clear_system_cache/BUILD.gn

Index: tools/perf/clear_system_cache/BUILD.gn
diff --git a/tools/perf/clear_system_cache/BUILD.gn b/tools/perf/clear_system_cache/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..34cfad3b435c92f9e19271c0a21dd8ba76f87903
--- /dev/null
+++ b/tools/perf/clear_system_cache/BUILD.gn
@@ -0,0 +1,19 @@
+# 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.
+
+if (is_linux && !is_chromeos) {
+  # TODO(GYP): Figure out which of these work and are needed on other platforms.
+  executable("clear_system_cache") {
+    testonly = true
+
+    sources = [
+      "clear_system_cache_main.cc",
+    ]
+
+    deps = [
+      "//base",
+      "//base/test:test_support",
+    ]
+  }
+}