Use gpu::Mailbox in IPCs instead of std::string

ui/compositor/compositor.h

Index: ui/compositor/compositor.h
diff --git a/ui/compositor/compositor.h b/ui/compositor/compositor.h
index 1f263e200f9b1ed6da7c5cfcfd7ba8b9ce2baf49..83c34b4d833f5fe020ccf1e6096596747f403a83 100644
--- a/ui/compositor/compositor.h
+++ b/ui/compositor/compositor.h
@@ -35,6 +35,10 @@ class Point;
 class Rect;
 }
 
+namespace gpu {
+struct Mailbox;
+}
+
 namespace WebKit {
 class WebGraphicsContext3D;
 }
@@ -128,12 +132,12 @@ class COMPOSITOR_EXPORT Texture : public base::RefCounted<Texture> {
   virtual WebKit::WebGraphicsContext3D* HostContext3D() = 0;
 
   // Replaces the texture with the texture from the specified mailbox.
-  virtual void Consume(const std::string& mailbox_name,
+  virtual void Consume(const gpu::Mailbox& mailbox_name,
                        const gfx::Size& new_size) {}
 
   // Moves the texture into the mailbox and returns the mailbox name.
   // The texture must have been previously consumed from a mailbox.
-  virtual std::string Produce();
+  virtual gpu::Mailbox Produce();
 
  protected:
   virtual ~Texture();