tree 2815f37ea295cacdb9dd091b7c65b38b75f76421
parent 47644068e19805e0131c53993726fdcb2ad8e142
author Stephen Li <stephenli@google.com> 1497663924 -0700
committer Stephen Li <stephenli@google.com> 1497909690 +0000

Handle diamond merges correctly.

If we have branches top, left, right, and bottom, and left == right,
then creating a change on top should create two changes with the same
sha on left and right, and only a single change on bottom.

top -> left -> bottom, and top -> right -> bottom simultaneously.

Change-Id: I8813cefb7cb7052b435dbef4e1af422c516e13a0