Avoid repeated code when building SVG help tables.

This saves roughly 6 KB of code.

  Grown symbols:
       +123: blink::SVGFontFaceElement::parseAttribute(blink::QualifiedName const&, WTF::AtomicString const&) type=t, (was 330 bytes, now 453 bytes)
  Removed symbols:
        -94: blink::mapAttributeToCSSProperty(WTF::HashMap<WTF::StringImpl*, blink::CSSPropertyID, WTF::StringHash, WTF::HashTraits<WTF::StringImpl*>, WTF::HashTraits<blink::CSSPropertyID>, WTF::DefaultAllocator>*, blink::QualifiedName const&) type=t, size=94 bytes
  Shrunk symbols:
      -2121: blink::SVGElement::animatedPropertyTypeForCSSAttribute(blink::QualifiedName const&) type=t, (was 3795 bytes, now 1674 bytes)
      -3786: blink::SVGElement::cssPropertyIdForSVGAttributeName(blink::QualifiedName const&) type=t, (was 5076 bytes, now 1290 bytes)

R=fs@opera.com
BUG=

Review URL: https://codereview.chromium.org/610593002

git-svn-id: svn://svn.chromium.org/blink/trunk@182903 bbb929c8-8fbe-4397-9dbb-9b2b20218538