- Adds an optional representation field to VReg and TestOperand structs.
- Adds a simple FP allocation test to register-allocator-unittest.cc.
- Adds some simple FP tests to move-optimizer-unittest.cc.

LOG=N
BUG=v8:4124

Review-Url: https://codereview.chromium.org/2400513002
Cr-Commit-Position: refs/heads/master@{#40117}