[arm64] Fix a string test in StringCompareStub.

This fixes a regression in Octane's pdf.js after r30818. The bug itself
has been present for a long time, but StringCompareStub wasn't actually
used until r30818 so it went unnoticed.

Review URL: https://codereview.chromium.org/1399983002

Cr-Commit-Position: refs/heads/master@{#31227}

src/arm64/macro-assembler-arm64.cc

@@ -2424,9 +2424,10 @@ void MacroAssembler::JumpIfEitherInstanceTypeIsNotSequentialOneByte(
     Label* failure) {
   DCHECK(!AreAliased(scratch1, second));
   DCHECK(!AreAliased(scratch1, scratch2));
-  static const int kFlatOneByteStringMask =
+  const int kFlatOneByteStringMask =
       kIsNotStringMask | kStringEncodingMask | kStringRepresentationMask;
-  static const int kFlatOneByteStringTag = ONE_BYTE_STRING_TYPE;
+  const int kFlatOneByteStringTag =
+      kStringTag | kOneByteStringTag | kSeqStringTag;
   And(scratch1, first, kFlatOneByteStringMask);
   And(scratch2, second, kFlatOneByteStringMask);
   Cmp(scratch1, kFlatOneByteStringTag);