blink/wtf: Make PartitionAlloc decommit test less strict.

This test fails on CFI bots, see attached bug. This is due to it being too
strict. It would be correct if there are no PA allocations triggered elsewhere
in the process, which is an assumption that can break with test harness changes.

Make the assert more tolerant to these changes, by asserting that memory is
reduced, instead of having a strict value.

Bug: 993219
Change-Id: I1e5e3b1f7e1f14357171a06a31a2eba9380babfe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1751183Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Benoit L <lizeb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#686357}

third_party/blink/renderer/platform/wtf/allocator/partitions_test.cc

@@ -49,7 +49,7 @@ TEST_F(PartitionsTest, Decommit) {
   EXPECT_GT(committed_after, committed_before);
   // Decommit works.
   base::PartitionAllocMemoryReclaimer::Instance()->Reclaim();
-  EXPECT_EQ(committed_before, Partitions::TotalSizeOfCommittedPages());
+  EXPECT_LT(Partitions::TotalSizeOfCommittedPages(), committed_after);
 }
 
 #endif  // !defined(MEMORY_TOOL_REPLACES_ALLOCATOR)