Turn libplatform into a component

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index b54d72b077a0eb7a6d338bebfd426117b2b06211..46f7210814dc66eec8bad0da3ab5645a3ee8c2a7 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -128,6 +128,9 @@ config("internal_config_base") {
 # This config should be applied to code using the libplatform.
 config("libplatform_config") {
   include_dirs = [ "include" ]
+  if (is_component_build) {
+    defines = [ "USING_V8_PLATFORM_SHARED" ]
+  }
 }
 
 # This config should be applied to code using the libsampler.
@@ -2280,9 +2283,10 @@ v8_source_set("v8_libbase") {
   # TODO(jochen): Add support for qnx, freebsd, openbsd, netbsd, and solaris.
 }
 
-v8_source_set("v8_libplatform") {
+v8_component("v8_libplatform") {
   sources = [
     "//base/trace_event/common/trace_event_common.h",
+    "include/libplatform/libplatform-export.h",
     "include/libplatform/libplatform.h",
     "include/libplatform/v8-tracing.h",
     "src/libplatform/default-platform.cc",
@@ -2302,6 +2306,10 @@ v8_source_set("v8_libplatform") {
 
   configs = [ ":internal_config_base" ]
 
+  if (is_component_build) {
+    defines = [ "BUILDING_V8_PLATFORM_SHARED" ]
+  }
+
   public_configs = [ ":libplatform_config" ]
 
   deps = [