Enable by default

Summary:
This enables Fast Refresh by default.

More concretely:

* For clean installs, it's enabled by default. (You can opt out at any time via the dev menu.)

* For updated DEV apps (on device or simulator), it flips from disabled to enabled **but only if you never touched the setting before**.

* If you previously explicitly enabled and/or later disabled it, we keep your previous setting.

Reviewed By: yungsters

Differential Revision: D16442656

fbshipit-source-id: 1bfe0bf4bcf2830284f9c757fbfacc10db92acb4

React/Modules/RCTDevSettings.mm

@@ -131,6 +131,7 @@ - (instancetype)init
   // default behavior is to use NSUserDefaults
   NSDictionary *defaultValues = @{
     kRCTDevSettingShakeToShowDevMenu: @YES,
+    kRCTDevSettingHotLoadingEnabled: @YES,
   };
   RCTDevSettingsUserDefaultsDataSource *dataSource = [[RCTDevSettingsUserDefaultsDataSource alloc] initWithDefaultValues:defaultValues];
   return [self initWithDataSource:dataSource];

ReactAndroid/src/main/java/com/facebook/react/devsupport/DevInternalSettings.java

@@ -107,7 +107,7 @@ public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, Strin
   }
 
   public boolean isHotModuleReplacementEnabled() {
-    return mPreferences.getBoolean(PREFS_HOT_MODULE_REPLACEMENT_KEY, false);
+    return mPreferences.getBoolean(PREFS_HOT_MODULE_REPLACEMENT_KEY, true);
   }
 
   public void setHotModuleReplacementEnabled(boolean enabled) {