Fix assigning NULL to scoped_refptr

Update code where NULL or 0 is assigned to a scoped_refptr to reset it. Just
call reset() instead. If operator=(std::nullptr_t) is added these assignments
become ambiguous.

This CL was uploaded by git cl split.

[email protected]

Bug: 1024981
Change-Id: Ia3973b95ed896197678e47de7697f68c3ab2e784
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1918156
Auto-Submit: kylechar <[email protected]>
Reviewed-by: Raymes Khoury <[email protected]>
Commit-Queue: kylechar <[email protected]>
Cr-Commit-Position: refs/heads/master@{#715710}
13 files changed