Enable asynchronous glReadPixels on Windows.

gpu/command_buffer/client/buffer_tracker.cc

Index: gpu/command_buffer/client/buffer_tracker.cc
diff --git a/gpu/command_buffer/client/buffer_tracker.cc b/gpu/command_buffer/client/buffer_tracker.cc
index 5887e52a71c458acbf998521e2a13299b1e46ac5..e405cbc5d6144f515058fd9693e37ab14d705634 100644
--- a/gpu/command_buffer/client/buffer_tracker.cc
+++ b/gpu/command_buffer/client/buffer_tracker.cc
@@ -21,16 +21,19 @@ BufferTracker::~BufferTracker() {
 }
 
 BufferTracker::Buffer* BufferTracker::CreateBuffer(
-    GLuint id, GLsizeiptr size) {
+    GLuint id, GLsizeiptr size, GLsizeiptr metadata_size) {
   DCHECK_NE(0u, id);
   DCHECK_LE(0, size);
+  DCHECK_LE(0, metadata_size);
   int32 shm_id = -1;
   uint32 shm_offset = 0;
   void* address = NULL;
-  if (size)
-    address = mapped_memory_->Alloc(size, &shm_id, &shm_offset);
+  const GLsizeiptr total_size = size + metadata_size;
+  if (total_size)
+    address = mapped_memory_->Alloc(total_size, &shm_id, &shm_offset);
 
-  Buffer* buffer = new Buffer(id, size, shm_id, shm_offset, address);
+  Buffer* buffer =
+      new Buffer(id, size, shm_id, shm_offset, address, metadata_size);
   std::pair<BufferMap::iterator, bool> result =
       buffers_.insert(std::make_pair(id, buffer));
   DCHECK(result.second);
@@ -60,6 +63,7 @@ void BufferTracker::FreePendingToken(Buffer* buffer, int32 token) {
   buffer->shm_id_ = 0;
   buffer->shm_offset_ = 0;
   buffer->address_ = NULL;
+  buffer->metadata_size_ = 0;
   buffer->last_usage_token_ = 0;
   buffer->last_async_upload_token_ = 0;
 }
@@ -69,6 +73,7 @@ void BufferTracker::Unmanage(Buffer* buffer) {
   buffer->shm_id_ = 0;
   buffer->shm_offset_ = 0;
   buffer->address_ = NULL;
+  buffer->metadata_size_ = 0;
   buffer->last_usage_token_ = 0;
   buffer->last_async_upload_token_ = 0;
 }
@@ -81,6 +86,7 @@ void BufferTracker::Free(Buffer* buffer) {
   buffer->shm_id_ = 0;
   buffer->shm_offset_ = 0;
   buffer->address_ = NULL;
+  buffer->metadata_size_ = 0;
   buffer->last_usage_token_ = 0;
   buffer->last_async_upload_token_ = 0;
 }