The main motivation is simplifying profiling activities:

1) Use hex instead of decimal for offsets, just like perf does. This
affects --print-opt-code

2) When printing block information, indicate loop information: if
block is header, where the end is; if block is in a loop, where the
loop starts. This affects --code-comments.

Using --print-opt-code --code-comments, and cross-referencing with data
obtained from perf, one may now find the block a hotspot belongs to
without needing to do hex2dec/dec2hex conversions. Once found, loop info
is available locally, on the block.

BUG=

Review URL: https://codereview.chromium.org/1177123002

Cr-Commit-Position: refs/heads/master@{#28964}