Add global flow types to eslint globals

Summary:
Added a subset of the global flow types from the fbjs eslint config to remove the no-undef errors for flow types as well as a few missing browser globals that were used in the codebase.

I also added a .eslintrc file to Examples to allow using alert there without warnings.
Closes https://github.com/facebook/react-native/pull/5585

Reviewed By: svcscm

Differential Revision: D2872016

Pulled By: vjeux

fb-gh-sync-id: f9b1b511289425393074b7237049dec38ea407b6

.eslintrc

@@ -19,6 +19,7 @@
     "__DEV__": true,
     "__dirname": false,
     "__fbBatchedBridgeConfig": false,
+    "alert": false,
     "cancelAnimationFrame": false,
     "clearImmediate": true,
     "clearInterval": false,
@@ -26,8 +27,11 @@
     "console": false,
     "document": false,
     "escape": false,
+    "Event": false,
+    "EventTarget": false,
     "exports": false,
     "fetch": false,
+    "FormData": false,
     "global": false,
     "jest": false,
     "Map": true,
@@ -43,7 +47,29 @@
     "setTimeout": false,
     "window": false,
     "XMLHttpRequest": false,
-    "pit": false
+    "pit": false,
+
+    // Flow global types.
+    "ReactComponent": false,
+    "ReactClass": false,
+    "ReactElement": false,
+    "ReactPropsCheckType": false,
+    "ReactPropsChainableTypeChecker": false,
+    "ReactPropTypes": false,
+    "SyntheticEvent": false,
+    "$Either": false,
+    "$All": false,
+    "$Tuple": false,
+    "$Supertype": false,
+    "$Subtype": false,
+    "$Shape": false,
+    "$Diff": false,
+    "$Keys": false,
+    "$Enum": false,
+    "$Exports": false,
+    "$FlowIssue": false,
+    "$FlowFixMe": false,
+    "$FixMe": false
   },
 
   "rules": {

Examples/.eslintrc

@@ -0,0 +1,5 @@
+{
+  "rules": {
+    "no-alert": 0
+  }
+}