Expose unstable_fileMapCacheManagerFactory and use it internally

Summary: Adds an `unstable_fileMapCacheManagerFactory` to config and passes it through to `metro-file-map`'s `cacheManagerFactory`

Reviewed By: motiz88

Differential Revision: D36697964

fbshipit-source-id: cf0ddcbbfd438d42c8c8dca208b05ef660db906e

Author: robhogan

packages/metro-config/src/configTypes.flow.js

@@ -13,6 +13,7 @@
 import type {IncomingMessage, ServerResponse} from 'http';
 import type {CacheStore} from 'metro-cache';
 import typeof MetroCache from 'metro-cache';
+import type {CacheManagerFactory} from 'metro-file-map';
 import type {CustomResolver} from 'metro-resolver';
 import type {MixedSourceMap} from 'metro-source-map';
 import type {JsTransformerConfig} from 'metro-transform-worker';
@@ -118,6 +119,7 @@ type MetalConfigT = {
   cacheVersion: string,
   fileMapCacheDirectory?: string,
   hasteMapCacheDirectory?: string, // Deprecated, alias of fileMapCacheDirectory
+  unstable_fileMapCacheManagerFactory?: CacheManagerFactory,
   maxWorkers: number,
   projectRoot: string,
   stickyWorkers: boolean,

packages/metro/src/node-haste/DependencyGraph/createHasteMap.js

@@ -56,13 +56,15 @@ function createHasteMap(
   const computeDependencies = dependencyExtractor != null;
 
   return MetroFileMap.create({
-    cacheManagerFactory: buildParameters =>
-      new DiskCacheManager({
-        buildParameters,
-        cacheDirectory:
-          config.fileMapCacheDirectory ?? config.hasteMapCacheDirectory,
-        cacheFilePrefix: options?.cacheFilePrefix,
-      }),
+    cacheManagerFactory:
+      config?.unstable_fileMapCacheManagerFactory ??
+      (buildParameters =>
+        new DiskCacheManager({
+          buildParameters,
+          cacheDirectory:
+            config.fileMapCacheDirectory ?? config.hasteMapCacheDirectory,
+          cacheFilePrefix: options?.cacheFilePrefix,
+        })),
     computeDependencies,
     computeSha1: true,
     dependencyExtractor: config.resolver.dependencyExtractor,