Make FencedAlloctor fail on size = 0.

gpu/command_buffer/client/fenced_allocator.cc

 // Copyright (c) 2011 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.
 
 // This file contains the implementation of the FencedAllocator class.
 
 #include "../client/fenced_allocator.h"
 #include <algorithm>
 #include "../client/cmd_buffer_helper.h"
 
@@ skipping 21 matching lines @@
   // GPU_DCHECK_EQ(blocks_.size(), 1u);
   // GPU_DCHECK_EQ(blocks_[0].state, FREE);
 }
 
 // Looks for a non-allocated block that is big enough. Search in the FREE
 // blocks first (for direct usage), first-fit, then in the FREE_PENDING_TOKEN
 // blocks, waiting for them. The current implementation isn't smart about
 // optimizing what to wait for, just looks inside the block in order (first-fit
 // as well).
 FencedAllocator::Offset FencedAllocator::Alloc(unsigned int size) {
-  // Similarly to malloc, an allocation of 0 allocates at least 1 byte, to
-  // return different pointers every time.
-  if (size == 0) size = 1;
+  // size of 0 is not allowed because it would be inconsistent to only sometimes
+  // have it succeed. Example: Alloc(SizeOfBuffer), Alloc(0).
+  if (size == 0)  {
+    return kInvalidOffset;
+  }
 
   // Try first to allocate in a free block.
   for (unsigned int i = 0; i < blocks_.size(); ++i) {
     Block &block = blocks_[i];
     if (block.state == FREE && block.size >= size) {
       return AllocInBlock(i, size);
     }
   }
 
   // No free block is available. Look for blocks pending tokens, and wait for
@@ skipping 148 matching lines @@
 // The blocks are in offset order, so we can do a binary search.
 FencedAllocator::BlockIndex FencedAllocator::GetBlockByOffset(Offset offset) {
   Block templ = { IN_USE, offset, 0, kUnusedToken };
   Container::iterator it = std::lower_bound(blocks_.begin(), blocks_.end(),
                                             templ, OffsetCmp());
   GPU_DCHECK(it != blocks_.end() && it->offset == offset);
   return it-blocks_.begin();
 }
 
 }  // namespace gpu