gpu: Associate all GpuMemoryBuffers with unique IDs.

ui/gfx/gpu_memory_buffer.cc

Index: ui/gfx/gpu_memory_buffer.cc
diff --git a/ui/gfx/gpu_memory_buffer.cc b/ui/gfx/gpu_memory_buffer.cc
index 18de4f0bd7c67ab0befb9a45ac8a0d0837caabf3..da80107bda452458eecc01419db935a595ae0d4a 100644
--- a/ui/gfx/gpu_memory_buffer.cc
+++ b/ui/gfx/gpu_memory_buffer.cc
@@ -8,14 +8,11 @@ namespace gfx {
 
 GpuMemoryBufferHandle::GpuMemoryBufferHandle()
     : type(EMPTY_BUFFER),
+      id(0),
       handle(base::SharedMemory::NULLHandle())
 #if defined(OS_MACOSX)
       ,
-      io_surface_id(0u)
-#endif
-#if defined(USE_X11)
-      ,
-      pixmap(0)
+      io_surface_id(0)
 #endif
 {
 }