Export some unix-specific content symbols

content/browser/renderer_host/backing_store_gtk.h

Index: content/browser/renderer_host/backing_store_gtk.h
diff --git a/content/browser/renderer_host/backing_store_gtk.h b/content/browser/renderer_host/backing_store_gtk.h
index f502bc36374f0f2c0603c99cb4a734c7b1eb42a3..0913434cc93d694744d206a427ca09737cbd38ed 100644
--- a/content/browser/renderer_host/backing_store_gtk.h
+++ b/content/browser/renderer_host/backing_store_gtk.h
@@ -9,6 +9,7 @@
 #include "base/basictypes.h"
 #include "build/build_config.h"
 #include "content/browser/renderer_host/backing_store.h"
+#include "content/common/content_export.h"
 #include "ui/base/x/x11_util.h"
 
 namespace gfx {
@@ -19,7 +20,7 @@ class Rect;
 typedef struct _GdkDrawable GdkDrawable;
 class SkBitmap;
 
-class BackingStoreGtk : public BackingStore {
+class CONTENT_EXPORT BackingStoreGtk : public BackingStore {
  public:
   // Create a backing store on the X server. The visual is an Xlib Visual
   // describing the format of the target window and the depth is the color