WIP: A couple of more ChannelMojo speedup ideas

third_party/mojo/src/mojo/edk/system/message_in_transit.h

Index: third_party/mojo/src/mojo/edk/system/message_in_transit.h
diff --git a/third_party/mojo/src/mojo/edk/system/message_in_transit.h b/third_party/mojo/src/mojo/edk/system/message_in_transit.h
index 9f118f9730b5549cf319de4f6d8f56c569e0ebfd..31332ed57f1f3f837f3c5e19a33d59150ef4050b 100644
--- a/third_party/mojo/src/mojo/edk/system/message_in_transit.h
+++ b/third_party/mojo/src/mojo/edk/system/message_in_transit.h
@@ -10,6 +10,7 @@
 
 #include <vector>
 
+#include "base/logging.h"
 #include "base/macros.h"
 #include "base/memory/aligned_memory.h"
 #include "base/memory/scoped_ptr.h"
@@ -142,6 +143,38 @@ class MOJO_SYSTEM_IMPL_EXPORT MessageInTransit {
     DISALLOW_COPY_AND_ASSIGN(View);
   };
 
+  class ReadContext {
+   public:
+    ReadContext(const View& view) : view_(view), passed_(false) {}
+
+    const View& view() {
+      DCHECK(!passed_);
+      return view_;
+    }
+
+    bool passed() const { return passed_; }
+    bool has_dispatchers() const { return dispatchers_.get(); }
+
+    void set_dispatchers(scoped_ptr<DispatcherVector> dispatchers) {
+      DCHECK(!passed_);
+      dispatchers_ = dispatchers.Pass();
+    }
+
+    scoped_ptr<MessageInTransit> PassMessage() {
+      DCHECK(!passed_);
+      passed_ = true;
+      scoped_ptr<MessageInTransit> message(new MessageInTransit(view_));
+      if (dispatchers_ != nullptr)
+        message->SetDispatchers(dispatchers_.Pass());
+      return message.Pass();
+    }
+
+   private:
+    const View& view_;
+    bool passed_;
+    scoped_ptr<DispatcherVector> dispatchers_;
+  };
+
   // |bytes| is optional; if null, the message data will be zero-initialized.
   MessageInTransit(Type type,
                    Subtype subtype,