[ios] Automatically fail any WebTest whose render process crashes.

ios/web/public/test/web_test.mm

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ios/web/public/test/web_test.h"
 
 #include "base/memory/ptr_util.h"
 #include "ios/web/public/active_state_manager.h"
+#include "ios/web/public/web_state/global_web_state_observer.h"
 #import "ios/web/public/test/fakes/test_web_client.h"
 
 namespace web {
 
-WebTest::WebTest() : web_client_(base::WrapUnique(new TestWebClient)) {}
+class WebTestRenderProcessCrashObserver : public GlobalWebStateObserver {
+ public:
+  WebTestRenderProcessCrashObserver() = default;
+  ~WebTestRenderProcessCrashObserver() override = default;
+
+  void RenderProcessGone(WebState* web_state) override {
+    FAIL() << "Renderer process died unexpectedly during the test";
+  }
+};
+
+WebTest::WebTest()
+    : web_client_(base::WrapUnique(new TestWebClient)),
+      crash_observer_(base::MakeUnique<WebTestRenderProcessCrashObserver>()) {}
 
 WebTest::~WebTest() {}
 
 void WebTest::SetUp() {
   PlatformTest::SetUp();
   BrowserState::GetActiveStateManager(&browser_state_)->SetActive(true);
 }
 
 void WebTest::TearDown() {
   BrowserState::GetActiveStateManager(&browser_state_)->SetActive(false);
   PlatformTest::TearDown();
 }
 
 TestWebClient* WebTest::GetWebClient() {
   return static_cast<TestWebClient*>(web_client_.Get());
 }
 
 BrowserState* WebTest::GetBrowserState() {
   return &browser_state_;
 }
 
+void WebTest::SetIgnoreRenderProcessCrashesDuringTesting(bool allow) {
+  if (allow) {
+    crash_observer_ = nullptr;
+  } else {
+    crash_observer_ = base::MakeUnique<WebTestRenderProcessCrashObserver>();
+  }
+}
+
 }  // namespace web