Fix IsAllocatorInitialized() for memory tools on Linux.
Fix IsAllocatorInitialized() for memory tools on Linux.

When MEMORY_TOOL_REPLACES_ALLOCATOR is defined, tcmalloc is not in use.

BUG=481611

Review URL: https://codereview.chromium.org/1846483002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#384084}

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