Adds a TransportDIB::Id value that is explicitly invalid and use it when compositing

app/surface/transport_dib.h

Index: app/surface/transport_dib.h
diff --git a/app/surface/transport_dib.h b/app/surface/transport_dib.h
index a55f624c54d08f6172155d89cd177cc360f0be02..71147fc7e87ce3c8a357ca8418d1a6f14c8d840c 100644
--- a/app/surface/transport_dib.h
+++ b/app/surface/transport_dib.h
@@ -95,7 +95,17 @@ class TransportDIB {
   }
 #elif defined(USE_X11)
   typedef int Handle;  // These two ints are SysV IPC shared memory keys
-  typedef int Id;
+  struct Id {
+    // Ensure that default initialized Ids are invalid.
+    Id() : shmkey(-1) {
+    }
+
+    bool operator< (const Id& other) const {

[brettw, 2011/03/24 23:54:34]

I think normal style would be no space afer the <

+      return shmkey < other.shmkey;
+    }
+
+    int shmkey;
+  };
 
   // Returns a default, invalid handle, that is meant to indicate a missing
   // Transport DIB.
@@ -129,7 +139,10 @@ class TransportDIB {
   static TransportDIB* CreateWithHandle(Handle handle);
 
   // Returns true if the handle is valid.
-  static bool is_valid(Handle dib);
+  static bool is_valid_handle(Handle dib);
+
+  // Returns true if the ID refers to a valid dib.
+  static bool is_valid_id(Id id);
 
   // Returns a canvas using the memory of this TransportDIB. The returned
   // pointer will be owned by the caller. The bitmap will be of the given size,
@@ -176,7 +189,7 @@ class TransportDIB {
   base::SharedMemory shared_memory_;
   uint32 sequence_num_;
 #elif defined(USE_X11)
-  int key_;  // SysV shared memory id
+  Id key_;  // SysV shared memory id
   void* address_;  // mapped address
   XSharedMemoryId x_shm_;  // X id for the shared segment
   Display* display_;  // connection to the X server