Kibana install metadata available as module

The metadata for the current kibana project install that is seeded to
the client-side app via window.__KBN__ is now accessible anywhere via
the immutable ui/metadata singleton. window.__KBN__ now becomes a tested
implementation detail of only a single module in the whole app, whereas
any consumer of the metadata now has an explicit module dependency and
has no way to modify the metadata contents.

src/plugins/testsBundle/testsEntryTemplate.js

@@ -21,6 +21,8 @@ ${pluginSlug}
  */
 
 window.__KBN__ = {
+  version: '1.2.3',
+  buildNum: 1234,
   vars: {
     kbnIndex: '.kibana',
     esShardTimeout: 1500,

src/ui/public/__tests__/metadata.js

@@ -0,0 +1,17 @@
+describe('ui/metadata', () => {
+  const expect = require('expect.js');
+
+  const metadata = require('ui/metadata');
+
+  it('is same data as window.__KBN__', () => {
+    expect(metadata.version).to.equal(window.__KBN__.version);
+    expect(metadata.vars.kbnIndex).to.equal(window.__KBN__.vars.kbnIndex);
+  });
+
+  it('is immutable', () => {
+    expect(() => metadata.foo = 'something').to.throw;
+    expect(() => metadata.version = 'something').to.throw;
+    expect(() => metadata.vars = {}).to.throw;
+    expect(() => metadata.vars.kbnIndex = 'something').to.throw;
+  });
+});

src/ui/public/chrome/chrome.js

@@ -8,6 +8,7 @@ require('ui/timefilter');
 require('ui/private');
 require('ui/promises');
 
+var metadata = require('ui/metadata');
 var TabCollection = require('ui/chrome/TabCollection');
 
 var chrome = {
@@ -17,7 +18,7 @@ var chrome = {
 };
 
 var internals = _.assign(
-  _.cloneDeep(window.__KBN__ || {}),
+  _.cloneDeep(metadata),
   {
     tabs: new TabCollection(),
     rootController: null,

src/ui/public/metadata.js

@@ -0,0 +1,24 @@
+// singleton for immutable copy of window.__KBN__
+define(function (require) {
+  const _ = require('lodash');
+
+  if (!_.has(window, '__KBN__')) {
+    throw new Error('window.__KBN__ must be set for metadata');
+  }
+
+  const kbn = _.cloneDeep(window.__KBN__ || {});
+  return deepFreeze(kbn);
+
+  function deepFreeze(object) {
+    // for any properties that reference an object, makes sure that object is
+    // recursively frozen as well
+    Object.keys(object).forEach(key => {
+      const value = object[key];
+      if (_.isObject(value)) {
+        deepFreeze(value);
+      }
+    });
+
+    return Object.freeze(object);
+  }
+});