port dd854449 (r28839)

original commit message:

    Boolean "is_strong" parameters have begun to proliferate across areas where
    strong mode semantics are different. This CL repurposes the existing
    ObjectStrength enum as a replacement for them.

BUG=
R=weiliang.lin@intel.com

Review URL: https://codereview.chromium.org/1173973002

Cr-Commit-Position: refs/heads/master@{#28952}