[regexp] do not assume short external strings have a minimum size.

test/cctest/cctest.status

 # Copyright 2011 the V8 project authors. All rights reserved.
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 # modification, are permitted provided that the following conditions are
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@@ skipping 68 matching lines @@
   # BUG(v8:4358). Hangs flakily.
   'test-debug/ProcessDebugMessagesThreaded': [SKIP],
 
   # BUG(2340). Preprocessing stack traces is disabled at the moment.
   'test-heap/PreprocessStackTrace': [FAIL],
 
   # BUG(4333). Function name inferrer does not work for ES6 clases.
   'test-func-name-inference/UpperCaseClass': [FAIL],
   'test-func-name-inference/LowerCaseClass': [FAIL],
 
+  # BUG(4923). MIPS64 port is missing.
+  'test-regexp/UncachedExternalString': [PASS, ['arch==mips64 or arch==mips64el', FAIL]],
+
   ##############################################################################
   # TurboFan compiler failures.
 
   # Some tests are just too slow to run for now.
   'test-heap/IncrementalMarkingStepMakesBigProgressWithLargeObjects': [PASS, NO_VARIANTS],
   'test-heap-profiler/ManyLocalsInSharedContext': [PASS, NO_VARIANTS],
   'test-serialize/CodeSerializerLargeCodeObject': [PASS, NO_VARIANTS],
   'test-debug/ThreadedDebugging': [PASS, NO_VARIANTS],
   # BUG(3742).
   'test-mark-compact/MarkCompactCollector': [PASS, ['arch==arm', NO_VARIANTS]],
@@ skipping 452 matching lines @@
   'test-run-inlining/InlineSurplusArguments': [FAIL],
   'test-run-inlining/InlineBuiltin': [FAIL],
   'test-run-inlining/InlineTwiceDependent': [FAIL],
   'test-run-inlining/SimpleInliningContextDeopt': [FAIL],
 
   # BUG(4751). Flaky with ignition and tsan.
   'test-cpu-profiler/JsNativeJsSample': [PASS, ['tsan', SKIP]],
 }],  # ignition == True
 
 ]