gpu: Allow BufferData size=0 for pixel transfer buffer objects.

gpu/command_buffer/client/buffer_tracker.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "../client/buffer_tracker.h"
 
 #include "../client/atomicops.h"
 #include "../client/cmd_buffer_helper.h"
 #include "../client/mapped_memory.h"
 
 namespace gpu {
 namespace gles2 {
 
 BufferTracker::BufferTracker(MappedMemoryManager* manager)
     : mapped_memory_(manager) {
 }
 
 BufferTracker::~BufferTracker() {
   while (!buffers_.empty()) {
     RemoveBuffer(buffers_.begin()->first);
   }
 }
 
 BufferTracker::Buffer* BufferTracker::CreateBuffer(
     GLuint id, GLsizeiptr size) {
   GPU_DCHECK_NE(0u, id);
-  GPU_DCHECK_LT(0, size);
-  int32 shm_id;
-  uint32 shm_offset;
-  void* address = mapped_memory_->Alloc(size, &shm_id, &shm_offset);
-  if (!address) {
-    return NULL;
+  GPU_DCHECK_LE(0, size);
+  int32 shm_id = -1;
+  uint32 shm_offset = 0;
+  void* address = NULL;
+  if (size) {
+    address = mapped_memory_->Alloc(size, &shm_id, &shm_offset);
+    if (!address) {
+      return NULL;
+    }
   }
 
   Buffer* buffer = new Buffer(id, size, shm_id, shm_offset, address);
   std::pair<BufferMap::iterator, bool> result =
       buffers_.insert(std::make_pair(id, buffer));
   GPU_DCHECK(result.second);
   return buffer;
 }
 
 BufferTracker::Buffer* BufferTracker::GetBuffer(GLuint client_id) {
   BufferMap::iterator it = buffers_.find(client_id);
   return it != buffers_.end() ? it->second : NULL;
 }
 
 void BufferTracker::RemoveBuffer(GLuint client_id) {
   BufferMap::iterator it = buffers_.find(client_id);
   if (it != buffers_.end()) {
     Buffer* buffer = it->second;
     buffers_.erase(it);
     if (buffer->address_)
       mapped_memory_->Free(buffer->address_);
     delete buffer;
   }
 }
 
 void BufferTracker::FreePendingToken(Buffer* buffer, int32 token) {
-  GPU_DCHECK(buffer->address_);
-  mapped_memory_->FreePendingToken(buffer->address_, token);
+  if (buffer->address_)
+    mapped_memory_->FreePendingToken(buffer->address_, token);
   buffer->size_ = 0;
   buffer->shm_id_ = 0;
   buffer->shm_offset_ = 0;
   buffer->address_ = NULL;
 }
 
 
 }  // namespace gles2
 }  // namespace gpu