code: public MethodDocImpl getMethodDoc(MethodSymbol meth) {
          assert !meth.isConstructor() : "not expecting a constructor symbol";
          MethodDocImpl result = (MethodDocImpl)methodMap.get(meth);
          if (result != null) return result;
          result = new MethodDocImpl(this, meth);
          methodMap.put(meth, result);
          return result;
      }
docs: Return the MethodDoc for a MethodSymbol.
  Should be called only on symbols representing methods.