Fix crash in WebAppIconDownloader::CancelDownloads()

It is possible for CancelDownloads() to be called after the callback_
has already been called via successful download or a previous
navigation. This CL adds a null check to avoid crashing in these corner
case scenarios.

Bug: 1059847
Change-Id: Idc97407ba67195beba51a9053ee2d71dcbd911f3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2102995Reviewed-by: Alexey Baskakov <loyso@chromium.org>
Commit-Queue: Alan Cutter <alancutter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#750466}

chrome/browser/web_applications/components/web_app_icon_downloader.cc

@@ -166,7 +166,8 @@ void WebAppIconDownloader::DidUpdateFaviconURL(
 void WebAppIconDownloader::CancelDownloads() {
   in_progress_requests_.clear();
   icons_map_.clear();
-  std::move(callback_).Run(/*success=*/false, icons_map_);
+  if (callback_)
+    std::move(callback_).Run(/*success=*/false, icons_map_);
 }
 
 }  // namespace web_app

chrome/browser/web_applications/components/web_app_icon_downloader_unittest.cc

@@ -298,6 +298,24 @@ TEST_F(WebAppIconDownloaderTest, PageNavigates) {
   EXPECT_FALSE(downloader.downloads_succeeded());
 }
 
+TEST_F(WebAppIconDownloaderTest, PageNavigatesAfterDownload) {
+  const GURL url("http://www.google.com/icon.png");
+  TestWebAppIconDownloader downloader(web_contents(), {url});
+  downloader.SkipPageFavicons();
+
+  downloader.Start();
+  EXPECT_EQ(1u, downloader.pending_requests());
+
+  downloader.CompleteImageDownload(0, 200, url, {gfx::Size(32, 32)});
+  EXPECT_EQ(0u, downloader.pending_requests());
+  EXPECT_TRUE(downloader.downloads_succeeded());
+
+  // Navigating the renderer after downloads have completed should not crash.
+  content::NavigationSimulator::CreateRendererInitiated(
+      GURL("https://foo.example"), main_rfh())
+      ->Commit();
+}
+
 TEST_F(WebAppIconDownloaderTest, PageNavigatesSameDocument) {
   content::NavigationSimulator::NavigateAndCommitFromBrowser(
       web_contents(), GURL("https://foo.example"));