38cc1fbc76b839ab6cb0d3d58f1ffa3d1de1e3bf  [Safer CPP] Address UncountedCallArgsChecker warnings in WebCore/loader/

Classified as not security-relevant.
Triage note: Adds nested protect() around frame()->document()/window()/navigationScheduler()/securityOrigin() and CachedImage m_image/begin() dereferences, plus SaferCPPExpectations removals. Blanket SaferCPP migration, no identified bug.
This commit was flagged by the signal scorer and reviewed by AI (not a human). It is listed only so the triage is auditable; there is no root-cause analysis because this is not a vulnerability fix.

Structural signals: smartptr_member_added (+4.87), area:Source/WebCore/loader (+2.0)