Convert components/tracing from static lib to component

components/tracing/BUILD.gn

Index: components/tracing/BUILD.gn
diff --git a/components/tracing/BUILD.gn b/components/tracing/BUILD.gn
index 336f5cb5ea487097480c3aec3cd95d37d22cc98e..b3186d94095df4a402b1a37a49256a97b50fdbd1 100644
--- a/components/tracing/BUILD.gn
+++ b/components/tracing/BUILD.gn
@@ -2,28 +2,34 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-source_set("tracing") {
+component("tracing") {
   sources = [
     "child_memory_dump_manager_delegate_impl.cc",
     "child_memory_dump_manager_delegate_impl.h",
     "child_trace_message_filter.cc",
     "child_trace_message_filter.h",
+    "tracing_export.h",
     "tracing_messages.cc",
     "tracing_messages.h",
   ]
 
+  defines = [ "TRACING_IMPLEMENTATION" ]
+
   deps = [
     "//base",
     "//ipc",
   ]
 }
 
-source_set("startup_tracing") {
+component("startup_tracing") {
   sources = [
     "startup_tracing.cc",
     "startup_tracing.h",
+    "tracing_export.h",
   ]
 
+  defines = [ "TRACING_IMPLEMENTATION" ]
+
   deps = [
     "//base",
   ]