Add LOG_TO_SINK_IF and DLOG_TO_SINK

[sukanth2705]

Added LOG_TO_SINK_IF and DLOG_TO_SINK in logging.h

This PR closes #568

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[sukanth2705]

@sergiud Can u take a look?

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 64.03%. Comparing base (570c7e4) to head (18bbf15). Report is 6 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1117 +/- ## ========================================== - Coverage 64.04% 64.03% -0.02% ========================================== Files 20 20 Lines 2578 2580 +2 Branches 898 908 +10 ========================================== + Hits 1651 1652 +1 - Misses 662 663 +1 Partials 265 265 ``` | [Files](https://app.codecov.io/gh/google/glog/pull/1117?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=google) | Coverage Δ | | |---|---|---| | [src/glog/logging.h](https://app.codecov.io/gh/google/glog/pull/1117?src=pr&el=tree&filepath=src%2Fglog%2Flogging.h&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=google#diff-c3JjL2dsb2cvbG9nZ2luZy5o) | `83.60% <ø> (ø)` | | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/google/glog/pull/1117/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=google)