gpu: Reuse transfer buffers more aggresively

gpu/command_buffer/client/fenced_allocator.h

Index: gpu/command_buffer/client/fenced_allocator.h
diff --git a/gpu/command_buffer/client/fenced_allocator.h b/gpu/command_buffer/client/fenced_allocator.h
index bb5c55170ab25e2766a4804c762a51ee00e8c2f3..55adea888bfa2a62a28948345bf01016f3ada7bc 100644
--- a/gpu/command_buffer/client/fenced_allocator.h
+++ b/gpu/command_buffer/client/fenced_allocator.h
@@ -65,6 +65,8 @@ class GPU_EXPORT FencedAllocator {
   //   token: the token value to wait for before re-using the memory.
   void FreePendingToken(Offset offset, int32 token);
 
+  void FreePendingSerial(Offset offset, uint32 token);
+
   // Frees any blocks pending a token for which the token has been read.
   void FreeUnused();
 
@@ -91,7 +93,8 @@ class GPU_EXPORT FencedAllocator {
   enum State {
     IN_USE,
     FREE,
-    FREE_PENDING_TOKEN
+    FREE_PENDING_TOKEN,
+    FREE_PENDING_SERIAL
   };
 
   // Book-keeping sturcture that describes a block of memory.
@@ -100,6 +103,7 @@ class GPU_EXPORT FencedAllocator {
     Offset offset;
     unsigned int size;
     int32 token;  // token to wait for in the FREE_PENDING_TOKEN case.
+    uint32 serial;
   };
 
   // Comparison functor for memory block sorting.
@@ -114,6 +118,7 @@ class GPU_EXPORT FencedAllocator {
   typedef unsigned int BlockIndex;
 
   static const int32 kUnusedToken = 0;
+  static const uint32 kUnusedSerial = 0;
 
   // Gets the index of a memory block, given its offset.
   BlockIndex GetBlockByOffset(Offset offset);
@@ -202,6 +207,11 @@ class FencedAllocatorWrapper {
     allocator_.FreePendingToken(GetOffset(pointer), token);
   }
 
+  void FreePendingSerial(void *pointer, uint32 serial) {
+    DCHECK(pointer);
+    allocator_.FreePendingSerial(GetOffset(pointer), serial);
+  }
+
   // Frees any blocks pending a token for which the token has been read.
   void FreeUnused() {
     allocator_.FreeUnused();