Restore ScopedLogger and add documentation.

third_party/WebKit/Source/wtf/wtf.gypi

 # For GN compatibility, this file can not have any conditions.
 {
     'variables': {
         'wtf_files': [
             'ASCIICType.cpp',
             'ASCIICType.h',
             'AddressSanitizer.h',
             'AddressSpaceRandomization.cpp',
             'AddressSpaceRandomization.h',
             'Alignment.h',
@@ skipping 184 matching lines @@
             'text/UTF8.h',
             'text/Unicode.h',
             'text/WTFString.cpp',
             'text/WTFString.h',
             'text/icu/CollatorICU.cpp',
             'text/icu/UnicodeIcu.h',
         ],
         'wtf_unittest_files': [
             'ASCIICTypeTest.cpp',
             'ArrayBufferBuilderTest.cpp',
+            'AssertionsTest.cpp',
             'DequeTest.cpp',
             'FunctionalTest.cpp',
             'HashMapTest.cpp',
             'HashSetTest.cpp',
             'ListHashSetTest.cpp',
             'MathExtrasTest.cpp',
             'OptionalTest.cpp',
             'PartitionAllocTest.cpp',
             'RefPtrTest.cpp',
             'SaturatedArithmeticTest.cpp',
             'StringExtrasTest.cpp',
             'StringHasherTest.cpp',
             'TemporaryChangeTest.cpp',
             'TreeNodeTest.cpp',
             'TypeTraitsTest.cpp',
             'VectorTest.cpp',
             'dtoa_test.cpp',
             'text/AtomicStringTest.cpp',
             'text/CStringTest.cpp',
             'text/StringBufferTest.cpp',
             'text/StringBuilderTest.cpp',
             'text/StringImplTest.cpp',
             'text/StringOperatorsTest.cpp',
             'text/TextCodecReplacementTest.cpp',
             'text/TextCodecUTF8Test.cpp',
             'text/WTFStringTest.cpp',
         ],
     },
 }