WTF_Ref.StaticReferenceCastFromRValueReference and WTF_RefPtr.Basic fail due to buffered logs of preceding tests

run-api-tests script runs each test separately by spawning processes.
But, if I manually run TestWTF.exe, some ref counter tests fail.

**PASS** WTF_Ref.StaticReferenceCastFromConstReference
**FAIL** WTF_Ref.StaticReferenceCastFromRValueReference

C:\home\webkit\gc\Tools\TestWebKitAPI\Tests\WTF\Ref.cpp:288
Expected equality of these values:
  "ref(a) "
  takeLogStr().c_str()
    Which is: "deref(a) deref(a) ref(a) "

**PASS** WTF_RefCountedFixedVector.Empty
**PASS** WTF_RefCountedFixedVector.Iterator
**PASS** WTF_RefCountedFixedVector.OverloadedOperatorAmpersand
**PASS** WTF_RefCountedFixedVector.Copy
**PASS** WTF_RefCountedFixedVector.CopyVector
**PASS** WTF_RefCountedFixedVector.MoveVector
**PASS** WTF_RefCountedFixedVector.IteratorFor
**PASS** WTF_RefCountedFixedVector.Reverse
**PASS** WTF_RefCountedFixedVector.Fill
**PASS** WTF_RefCountedFixedVector.Destructor
**PASS** WTF_RefCountedFixedVector.DestructorAfterMove
**PASS** WTF_RefCountedFixedVector.Basic
**PASS** WTF_RefCountedFixedVector.Clone
**PASS** WTF_RefCountedFixedVector.Equal
**FAIL** WTF_RefPtr.Basic

C:\home\webkit\gc\Tools\TestWebKitAPI\Tests\WTF\RefPtr.cpp:53
Expected equality of these values:
  "ref(a) deref(a) "
  takeLogStr().c_str()
    Which is: "deref(a) ref(a) deref(a) "

**PASS** WTF_RefPtr.AssignPassRefToRefPtr