Dry up multiplication and division of equation members

packages/cassowary/lib/constant_member.dart

@@ -9,14 +9,6 @@ class ConstantMember extends EquationMember {
   ConstantMember(this.value);
 
   Expression asExpression() => new Expression([], this.value);
-
-  EquationMember operator *(double m) {
-    return new ConstantMember(this.value * m);
-  }
-
-  EquationMember operator /(double m) {
-    return new ConstantMember(this.value / m);
-  }
 }
 
 ConstantMember CM(num value) {

packages/cassowary/lib/equation_member.dart

@@ -16,4 +16,8 @@ abstract class EquationMember {
   Expression operator +(EquationMember m) => asExpression() + m;
 
   Expression operator -(EquationMember m) => asExpression() - m;
+
+  Expression operator *(double m) => asExpression() * m;
+
+  Expression operator /(double m) => asExpression() / m;
 }

packages/cassowary/lib/expression.dart

@@ -105,13 +105,12 @@ class Expression extends EquationMember {
   EquationMember operator *(double m) {
     var terms = this.terms.fold(new List<Term>(), (list, term) => list
       ..add(new Term(term.variable, term.coefficient * m)));
-    return new Expression(terms, this.constant);
+    return new Expression(terms, this.constant * m);
   }
 
-  // TODO(csg): Figure out how to dry this up.
   EquationMember operator /(double m) {
     var terms = this.terms.fold(new List<Term>(), (list, term) => list
       ..add(new Term(term.variable, term.coefficient / m)));
-    return new Expression(terms, this.constant);
+    return new Expression(terms, this.constant / m);
   }
 }

packages/cassowary/lib/term.dart

@@ -13,12 +13,4 @@ class Term extends EquationMember {
 
   Expression asExpression() =>
       new Expression([new Term(this.variable, this.coefficient)], 0.0);
-
-  EquationMember operator *(double m) {
-    return new Term(this.variable, this.coefficient * m);
-  }
-
-  EquationMember operator /(double m) {
-    return new Term(this.variable, this.coefficient / m);
-  }
 }

packages/cassowary/lib/variable.dart

@@ -9,12 +9,4 @@ class Variable extends EquationMember {
   Variable(this.value);
 
   Expression asExpression() => new Expression([new Term(this, 1.0)], 0.0);
-
-  EquationMember operator *(double m) {
-    return new Term(this, m);
-  }
-
-  EquationMember operator /(double m) {
-    return new Term(this, 1.0 / m);
-  }
 }