Fix uninitialized pointer in unit tests.

chrome/browser/android/offline_pages/prerendering_offliner_unittest.cc

 // 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 "chrome/browser/android/offline_pages/prerendering_offliner.h"
 
 #include <memory>
 
 #include "base/bind.h"
 #include "base/run_loop.h"
@@ skipping 27 matching lines @@
 
 // Mock Loader for testing the Offliner calls.
 class MockPrerenderingLoader : public PrerenderingLoader {
  public:
   explicit MockPrerenderingLoader(content::BrowserContext* browser_context)
       : PrerenderingLoader(browser_context),
         can_prerender_(true),
         mock_loading_(false),
         mock_loaded_(false),
         mock_is_lowbar_met_(false),
-        start_snapshot_called_(false) {}
+        start_snapshot_called_(false),
+        web_contents_(nullptr) {}
   ~MockPrerenderingLoader() override { delete web_contents_; }
 
   bool LoadPage(const GURL& url,
                 const LoadPageCallback& load_done_callback,
                 const ProgressCallback& progress_callback) override {
     mock_loading_ = can_prerender_;
     load_page_callback_ = load_done_callback;
     progress_callback_ = progress_callback;
     return mock_loading_;
   }
@@ skipping 551 matching lines @@
   PumpLoop();
   EXPECT_EQ(Offliner::RequestStatus::SAVED, request_status());
 
   // One extra part should be added if the flag is on.
   content::MHTMLExtraParts* extra_parts =
       content::MHTMLExtraParts::FromWebContents(loader()->web_contents());
   EXPECT_EQ(extra_parts->size(), 1);
 }
 
 }  // namespace offline_pages