Add GLES2Implemention::FreeUnusedSharedMemory

gpu/command_buffer/client/fenced_allocator.cc

Index: gpu/command_buffer/client/fenced_allocator.cc
diff --git a/gpu/command_buffer/client/fenced_allocator.cc b/gpu/command_buffer/client/fenced_allocator.cc
index f105f3a50ea3e23b6045f798831af085aebd3e2b..912c22dd6cbf4e285af07c386593f0eef78f1b6a 100644
--- a/gpu/command_buffer/client/fenced_allocator.cc
+++ b/gpu/command_buffer/client/fenced_allocator.cc
@@ -130,6 +130,10 @@ bool FencedAllocator::CheckConsistency() {
   return true;
 }
 
+bool FencedAllocator::InUse() {
+  return blocks_.size() != 1 || blocks_[0].state != FREE;
+}
+
 // Collapse the block to the next one, then to the previous one. Provided the
 // structure is consistent, those are the only blocks eligible for collapse.
 FencedAllocator::BlockIndex FencedAllocator::CollapseFreeBlock(