Summary:
**Motivation**
On Exponent we load fonts dynamically and assign their native names by appending a session id, so that fonts from one Exponent "experience" do not clash with each other. So, before sending the `fontFamily` to native, we want to change it to the Exponent-scoped `fontFamily`.
Example:
```js
// Before rendering your app
StyleSheet.setStyleAttributePreprocessor('fontFamily', _processFontFamily);
function _processFontFamily(name) {
// Pass system fonts through
if (!name || Constants.systemFonts.indexOf(name) >= 0) {
return name;
}
if (!Font.isLoaded(name)) {
if (__DEV__) {
console.error(`${name} is not a system font and has not been loaded through Exponent.Font.loadAsync. If you intended to use a system font, make sure you typed the name correctly and that it is supported by the current operating system. If this is a custom font, be sure to load it with Exponent.Font.loadAsync`);
} else {
return 'system';
}
}
return `ExponentFont-
Closes https://github.com/facebook/react-native/pull/11138
Differential Revision: D4245518
Pulled By: mkonicek
fbshipit-source-id: bd2452b1129d6675aa7b88e41351f8bb61fa20a3
346858a552