[gin] Turn gin into a component

gin/public/context_holder.h

Index: gin/public/context_holder.h
diff --git a/gin/public/context_holder.h b/gin/public/context_holder.h
index 43b2822882dfc360768e27ca6bbf6770383bb921..09fe248a373d0d77be1f61a4254419c78e8ab317 100644
--- a/gin/public/context_holder.h
+++ b/gin/public/context_holder.h
@@ -9,6 +9,7 @@
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
+#include "gin/gin_export.h"
 #include "v8/include/v8.h"
 
 namespace gin {
@@ -27,7 +28,7 @@ class PerContextData;
 // ContextHolder is a generic class for holding a v8::Context. Rather than
 // using ContextHolder directly, most code should use a subclass of
 // ContextHolder, such as Runner.
-class ContextHolder {
+class GIN_EXPORT ContextHolder {
  public:
   explicit ContextHolder(v8::Isolate* isolate);
   ~ContextHolder();