Make WebTraceLocation be an alias of tracked_objects::Location

Make WebTraceLocation be an alias of tracked_objects::Location and
BLINK_FROM_HERE be an alias of FROM_HERE as well. So that tasks posted
from Blink leaves a valid program counter and line number in the crash
dump.

Review-Url: https://codereview.chromium.org/2137013002
Cr-Commit-Position: refs/heads/master@{#405736}
22 files changed