[ios] Added DialogsSuppression public API to WebState.

ios/web/public/test/test_web_state.mm

Index: ios/web/public/test/test_web_state.mm
diff --git a/ios/web/public/test/test_web_state.mm b/ios/web/public/test/test_web_state.mm
index 9d9ef40406c0a8dc7fec2f610caeda567e109362..befb12bdc5ebb3b309ea990ce967cdc87f1a92b3 100644
--- a/ios/web/public/test/test_web_state.mm
+++ b/ios/web/public/test/test_web_state.mm
@@ -36,6 +36,12 @@ void TestWebState::SetWebUsageEnabled(bool enabled) {
   web_usage_enabled_ = enabled;
 }
 
+bool TestWebState::ShouldSuppressDialogs() const {
+  return false;
+}
+
+void TestWebState::SetShouldSuppressDialogs(bool should_suppress) {}
+
 UIView* TestWebState::GetView() {
   return nullptr;
 }