Recent changes in Segment class caused many tests to fail on mips32
because of an unaligned read error. Setting the alignment to 8 for mips
fixes the issue. Accessing doubles on mips32 must be eight bit aligned.

BUG=

Review-Url: https://codereview.chromium.org/2390303003
Cr-Commit-Position: refs/heads/master@{#40039}