MIPS: Skip test-heap/TestSizeOfRegExpCode

After https://codereview.chromium.org/1180433003 the code-size exceeeds
the limit for MIPS. We have some optimizations in place for MIPS64 that
will be ported back to MIPS, and will investigate other code-size
improvements so we can re-enable this test.

BUG=

Review URL: https://codereview.chromium.org/1166353005

Cr-Commit-Position: refs/heads/master@{#28913}

test/cctest/cctest.status

@@ -261,6 +261,9 @@
 ['arch == mipsel or arch == mips', {
   'test-cpu-profiler/CollectDeoptEvents': [PASS, FAIL],
 
+  # TODO(mips-team): Improve code-size on large RegExp's.
+  'test-heap/TestSizeOfRegExpCode':  [SKIP],
+
   # BUG(1075): Unresolved crashes on MIPS also.
   'test-serialize/Deserialize': [SKIP],
   'test-serialize/DeserializeFromSecondSerializationAndRunScript2': [SKIP],