Add a "started" protected property to BrowserCoordinator.

ios/clean/chrome/browser/browser_coordinator+internal.h

Index: ios/clean/chrome/browser/browser_coordinator+internal.h
diff --git a/ios/clean/chrome/browser/browser_coordinator+internal.h b/ios/clean/chrome/browser/browser_coordinator+internal.h
index 06315554a0e069006b5df9a7d672015fffd654f5..48f7ea271bdf2aab3af35bc644a09e9ce75d2748 100644
--- a/ios/clean/chrome/browser/browser_coordinator+internal.h
+++ b/ios/clean/chrome/browser/browser_coordinator+internal.h
@@ -37,6 +37,10 @@
 // The coordinator that added this coordinator as a child, if any.
 @property(nonatomic, readonly) BrowserCoordinator* parentCoordinator;
 
+// YES if the receiver has been started; NO (the default) otherwise. Stopping
+// the receiver resets this property to NO.
+@property(nonatomic, readonly) BOOL started;
+
 // YES if the receiver is acting as an overlay coordinator; NO (the default)
 // otherwise.
 @property(nonatomic, readonly) BOOL overlaying;