Port 2fd55667

Original commit message:

    We ported hashmap.h into libsampler as a workaround before, so the main focus of
    this patch is to reduce code duplication. This patch moves the hashmap into
    src/base as well as creates DefaultAllocationPolicy using malloc and free.

R=lpy@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com, mbrandy@us.ibm.com

BUG=v8:5050
LOG=N

Review-Url: https://codereview.chromium.org/2057263002
Cr-Commit-Position: refs/heads/master@{#36900}