[ios] Added WebState::GetLoadingProgress web// API.

ios/web/web_state/ui/crw_web_controller.h

Index: ios/web/web_state/ui/crw_web_controller.h
diff --git a/ios/web/web_state/ui/crw_web_controller.h b/ios/web/web_state/ui/crw_web_controller.h
index 1dea724ca0e780625ca57933567a8f3d76edb020..7e2acde0c20c97b855fca8642b6667bae7abd472 100644
--- a/ios/web/web_state/ui/crw_web_controller.h
+++ b/ios/web/web_state/ui/crw_web_controller.h
@@ -98,6 +98,10 @@ class WebStateImpl;
 // Returns the current page loading phase.
 @property(nonatomic, readonly) web::LoadPhase loadPhase;
 
+// The fraction of the page load that has completed as a number between 0.0
+// (nothing loaded) and 1.0 (fully loaded).
+@property(nonatomic, readonly) double loadingProgress;
+
 // Returns whether the page can navigate backwards or forwards.
 @property(nonatomic, readonly) BOOL canGoBack;
 @property(nonatomic, readonly) BOOL canGoForward;