Add export directives needed by Chromium WM project.

content/browser/gpu/browser_gpu_channel_host_factory.h

Index: content/browser/gpu/browser_gpu_channel_host_factory.h
diff --git a/content/browser/gpu/browser_gpu_channel_host_factory.h b/content/browser/gpu/browser_gpu_channel_host_factory.h
index f9290bb3c71be729622d684b446d868aa40e213e..a410868b35bdea07a58ba673b5791309a90181de 100644
--- a/content/browser/gpu/browser_gpu_channel_host_factory.h
+++ b/content/browser/gpu/browser_gpu_channel_host_factory.h
@@ -9,12 +9,14 @@
 #include "base/memory/scoped_ptr.h"
 #include "base/process.h"
 #include "base/synchronization/waitable_event.h"
+#include "content/common/content_export.h"
 #include "content/common/gpu/client/gpu_channel_host.h"
 #include "ipc/ipc_channel_handle.h"
 
 namespace content {
 
-class BrowserGpuChannelHostFactory : public GpuChannelHostFactory {
+class CONTENT_EXPORT BrowserGpuChannelHostFactory :
+    public GpuChannelHostFactory {
  public:
   static void Initialize();
   static void Terminate();