Sync the Flow tests (#1163)

* Extract custom tests from tests/flow/

Approach:

1. Remove all .js files in tests/flow except .snap.js files.
2. Copy over all .js files from tests/ in the flow repo.
3. Go through the diff looking for deletions.
   - It was easy to see which deletions were due to changes in the tests
     due to updates in the flow repo.
   - For the rest of the deletions, I used `git blame` to verify that
     they had been added by us since the flow tests were copied over.

This makes tests/flow/ simply a copy of the tests from the flow repo,
making it easier to sync with the upstream flow tests in the future.

* Add a script for syncing the flow tests

* Sync the flow tests

tests/flow_array_comments/__snapshots__/jsfmt.spec.js.snap

@@ -0,0 +1,22 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`test.js 1`] = `
+"export type FileMetaData = [
+  /* id */ string,
+  /* mtime */ number,
+  /* visited */ 0|1,
+  /* dependencies */ Array<string>,
+];
+
+export type ModuleMetaData = [Path, /* type */ number];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+export type FileMetaData = [
+  /* id */ string,
+  /* mtime */ number,
+  /* visited */ 0 | 1,
+  /* dependencies */ Array<string>
+];
+
+export type ModuleMetaData = [Path, /* type */ number];
+"
+`;

tests/flow_array_comments/jsfmt.spec.js

@@ -0,0 +1 @@
+run_spec(__dirname);

tests/flow_array_comments/test.js

@@ -0,0 +1,8 @@
+export type FileMetaData = [
+  /* id */ string,
+  /* mtime */ number,
+  /* visited */ 0|1,
+  /* dependencies */ Array<string>,
+];
+
+export type ModuleMetaData = [Path, /* type */ number];