AU: Nit I forgot to check in (TBR)

BUG=chromium-os:6390
TEST=None

Review URL: http://codereview.chromium.org/3367010
diff --git a/delta_diff_generator.cc b/delta_diff_generator.cc
index 4433c1f..679f095 100644
--- a/delta_diff_generator.cc
+++ b/delta_diff_generator.cc
@@ -453,7 +453,7 @@
 
   op->set_dst_length(new_part_size);
 
-  // Theres a single dest extent
+  // There's a single dest extent
   Extent* dst_extent = op->add_dst_extents();
   dst_extent->set_start_block(0);
   dst_extent->set_num_blocks((new_part_size + kBlockSize - 1) / kBlockSize);