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_function_parentheses/__snapshots__/jsfmt.spec.js.snap

@@ -0,0 +1,68 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`test.js 1`] = `
+"type Banana = {
+  eat: string => boolean,
+};
+
+type Hex = {n: 0x01};
+
+type T = { method: (a) => void };
+
+type T = { method(a): void };
+
+declare class X { method(a): void }
+
+declare function f(a): void;
+
+var f: (a) => void;
+
+interface F { m(string): number }
+
+interface F { m: (string) => number }
+
+function f(o: { f: (string) => void }) {}
+
+function f(o: { f(string): void }) {}
+
+type f = (...arg) => void;
+
+type f = (/* comment */ arg) => void;
+
+type f = (arg /* comment */) => void;
+
+type f = (?arg) => void;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+type Banana = {
+  eat: string => boolean
+};
+
+type Hex = { n: 0x01 };
+
+type T = { method: a => void };
+
+type T = { method(a): void };
+
+declare class X { method(a): void }
+
+declare function f(a): void;
+
+var f: a => void;
+
+interface F { m(string): number }
+
+interface F { m: string => number }
+
+function f(o: { f: string => void }) {}
+
+function f(o: { f(string): void }) {}
+
+type f = (...arg) => void;
+
+type f = /* comment */ arg => void;
+
+type f = arg /* comment */ => void;
+
+type f = ?arg => void;
+"
+`;

tests/flow_function_parentheses/jsfmt.spec.js

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

tests/flow_function_parentheses/test.js

@@ -0,0 +1,31 @@
+type Banana = {
+  eat: string => boolean,
+};
+
+type Hex = {n: 0x01};
+
+type T = { method: (a) => void };
+
+type T = { method(a): void };
+
+declare class X { method(a): void }
+
+declare function f(a): void;
+
+var f: (a) => void;
+
+interface F { m(string): number }
+
+interface F { m: (string) => number }
+
+function f(o: { f: (string) => void }) {}
+
+function f(o: { f(string): void }) {}
+
+type f = (...arg) => void;
+
+type f = (/* comment */ arg) => void;
+
+type f = (arg /* comment */) => void;
+
+type f = (?arg) => void;