Account for MathML tags / attributes in staticQualifiedNamesCount

Account for MathML tags / attributes in staticQualifiedNamesCount in
QualifiedName.cpp. This code was removed in r149242 when MathML support was
partially removed. However, MathMLNames.h is still generated and used in the
code base so we should still account for those static QualifiedNames.

This avoids unnecessary hash table expansion and rehashing due to
minimumTableSize HashTraits variable being inaccurate.

R=eseidel@chromium.org, adamk@chromium.org
BUG=236462

Review URL: https://codereview.chromium.org/485053002

git-svn-id: svn://svn.chromium.org/blink/trunk@180587 bbb929c8-8fbe-4397-9dbb-9b2b20218538