[XLA/GPU] Address review comments.

tensorflow/compiler/xla/debug_options_flags.cc

@@ -580,7 +580,8 @@ static void AllocateFlags() {
       "Generates multiple heaps (i.e., temp buffers) with a size "
       "constraint on each heap to avoid Out-of-Memory due to memory "
       "fragmentation. The constraint is soft, so it works with tensors "
-      "larger than the given constraint size."));
+      "larger than the given constraint size. -1 corresponds to no "
+      "constraints."));
 
   ParseFlagsFromEnvAndDieIfUnknown("XLA_FLAGS", *flag_objects);
 }

tensorflow/compiler/xla/service/buffer_assignment.cc

@@ -608,7 +608,7 @@ void BufferAssignment::AddAssignment(BufferAllocation* allocation,
 void BufferAssignment::CombineTempAllocations() {
   VLOG(1) << "CombineTempAllocations()";
   // Stores the combined allocations.
-  std::vector<BufferAllocation> combined_allocations;
+  std::deque<BufferAllocation> combined_allocations;
   // Holds the pointer to a combined allocation of each color, if any.
   flat_hash_map<BufferValue::Color, BufferAllocation*> combined_allocation_map;