Make base a static ibrary

base/trace_event/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.
 
-source_set("trace_event") {
+# Should be static library, see documentation on //base:base for discussion.
+static_library("trace_event") {
   sources = [
     "common/trace_event_common.h",
     "heap_profiler_allocation_context.cc",
     "heap_profiler_allocation_context.h",
     "heap_profiler_allocation_context_tracker.cc",
     "heap_profiler_allocation_context_tracker.h",
     "heap_profiler_allocation_register.cc",
     "heap_profiler_allocation_register.h",
     "heap_profiler_allocation_register_posix.cc",
     "heap_profiler_allocation_register_win.cc",
@@ skipping 123 matching lines @@
   if (is_android) {
     sources += [ "trace_event_android_unittest.cc" ]
   }
 
   deps = [
     "//base/test:test_support",
     "//testing/gmock",
     "//testing/gtest",
   ]
 }