Work around limitations of React Native Map/Set polyfills.

As explained here, with astonishing honesty:
https://github.com/facebook/react-native/blob/98a6f19d7c41e1d4fd3c04d07bb2c4e627f21724/Libraries/vendor/core/Map.js#L44-L50

As reported most recently here:
apollographql/react-apollo#2442 (comment)

For the record, I have previously complained that these polyfills are
simply buggy and should be replaced:
#3394 (comment)

While that is still true, this workaround should moot the debate. 🐮

packages/apollo-cache-inmemory/src/fixPolyfills.ts

@@ -0,0 +1,32 @@
+const frozen = {};
+const frozenTestMap = new Map();
+
+if (typeof Object.freeze === 'function') {
+  Object.freeze(frozen);
+}
+
+try {
+  // If non-extensible objects can't be stored as keys in a Map, make sure we
+  // do not freeze/seal/etc. an object without first attempting to put it in a
+  // Map. For example, this gives the React Native Map polyfill a chance to tag
+  // objects before they become non-extensible:
+  // https://github.com/facebook/react-native/blob/98a6f19d7c/Libraries/vendor/core/Map.js#L44-L50
+  // https://github.com/apollographql/react-apollo/issues/2442#issuecomment-426489517
+  frozenTestMap.set(frozen, frozen).delete(frozen);
+} catch {
+  const wrap = (method: <T>(obj: T) => T): typeof method => {
+    return method && (obj => {
+      try {
+        // If .set succeeds, also call .delete to avoid leaking memory.
+        frozenTestMap.set(obj, obj).delete(obj);
+      } finally {
+        // If .set or .delete fails, the exception will be silently swallowed
+        // by this return-from-finally statement:
+        return method.call(Object, obj);
+      }
+    });
+  };
+  Object.freeze = wrap(Object.freeze);
+  Object.seal = wrap(Object.seal);
+  Object.preventExtensions = wrap(Object.preventExtensions);
+}

packages/apollo-cache-inmemory/src/inMemoryCache.ts

@@ -1,3 +1,6 @@
+// Make builtins like Map and Set safe to use with non-extensible objects.
+import './fixPolyfills';
+
 import { DocumentNode } from 'graphql';
 
 import { Cache, DataProxy, ApolloCache, Transaction } from 'apollo-cache';