Turn libplatform into a component

include/libplatform/libplatform.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_LIBPLATFORM_LIBPLATFORM_H_
 #define V8_LIBPLATFORM_LIBPLATFORM_H_
 
+#include "libplatform/libplatform-export.h"
 #include "libplatform/v8-tracing.h"
 #include "v8-platform.h"  // NOLINT(build/include)
 
 namespace v8 {
 namespace platform {
 
 /**
  * Returns a new instance of the default v8::Platform implementation.
  *
  * The caller will take ownership of the returned pointer. |thread_pool_size|
  * is the number of worker threads to allocate for background jobs. If a value
  * of zero is passed, a suitable default based on the current number of
  * processors online will be chosen.
  */
-v8::Platform* CreateDefaultPlatform(int thread_pool_size = 0);
-
+V8_PLATFORM_EXPORT v8::Platform* CreateDefaultPlatform(
+    int thread_pool_size = 0);
 
 /**
  * Pumps the message loop for the given isolate.
  *
  * The caller has to make sure that this is called from the right thread.
  * Returns true if a task was executed, and false otherwise. This call does
  * not block if no task is pending. The |platform| has to be created using
  * |CreateDefaultPlatform|.
  */
-bool PumpMessageLoop(v8::Platform* platform, v8::Isolate* isolate);
+V8_PLATFORM_EXPORT bool PumpMessageLoop(v8::Platform* platform,
+                                        v8::Isolate* isolate);
 
 /**
  * Attempts to set the tracing controller for the given platform.
  *
  * The |platform| has to be created using |CreateDefaultPlatform|.
  */
-void SetTracingController(
+V8_PLATFORM_EXPORT void SetTracingController(
     v8::Platform* platform,
     v8::platform::tracing::TracingController* tracing_controller);
 
 }  // namespace platform
 }  // namespace v8
 
 #endif  // V8_LIBPLATFORM_LIBPLATFORM_H_