Add rule to enforce one provide per file

rules/one-provide.js

@@ -0,0 +1,28 @@
+'use strict';
+
+const util = require('./util');
+
+exports.rule = {
+  meta: {
+    docs: {
+      description: 'disallow multiple goog.provide() calls'
+    }
+  },
+
+  create: function(context) {
+    let hasProvide = false;
+
+    return {
+      ExpressionStatement: function(statement) {
+        if (util.isProvideStatement(statement)) {
+          if (hasProvide) {
+            const name = statement.expression.arguments[0].value;
+            context.report(statement, `Extra goog.provide('${name}')`);
+          } else {
+            hasProvide = true;
+          }
+        }
+      }
+    };
+  }
+};