Lazily create a TestingProfile in OptimizationGuideHintsManagerTest

This currently crashes on Android O builders when we intend to move
the clock forward since the queue flushes all pending tasks and one of
the tasks that gets posted at the end of startup attempts that the
creation of a TestingProfile triggers is to instantiate a
system_network_context_manager which is null in unit tests.
(crbug/981057)

Bug: 999349
Change-Id: Ie60ca11674eb332a277dc783181f0230c7a23ef5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1788300Reviewed-by: Doug Arnett <dougarnett@chromium.org>
Commit-Queue: Sophie Chang <sophiechang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#693943}

chrome/browser/optimization_guide/optimization_guide_hints_manager_unittest.cc

@@ -316,8 +316,11 @@ class OptimizationGuideHintsManagerTest
   std::unique_ptr<content::MockNavigationHandle>
   CreateMockNavigationHandleWithOptimizationGuideWebContentsObserver(
       const GURL& url) {
+    if (!testing_profile_) {
+      testing_profile_ = std::make_unique<TestingProfile>();
+    }
     content::WebContents* web_contents =
-        web_contents_factory_->CreateWebContents(&testing_profile_);
+        web_contents_factory_->CreateWebContents(testing_profile_.get());
     OptimizationGuideWebContentsObserver::CreateForWebContents(web_contents);
     std::unique_ptr<content::MockNavigationHandle> navigation_handle =
         std::make_unique<content::MockNavigationHandle>(web_contents);
@@ -371,7 +374,7 @@ class OptimizationGuideHintsManagerTest
   content::BrowserTaskEnvironment task_environment_{
       base::test::TaskEnvironment::MainThreadType::UI,
       base::test::TaskEnvironment::TimeSource::MOCK_TIME};
-  TestingProfile testing_profile_;
+  std::unique_ptr<TestingProfile> testing_profile_;
   std::unique_ptr<content::TestWebContentsFactory> web_contents_factory_;
   std::unique_ptr<OptimizationGuideHintsManager> hints_manager_;
   std::unique_ptr<TestOptimizationGuideService> optimization_guide_service_;