Disable DownloadImage_*_FileImage due to flakiness

Disabled two tests:
- WebContentsImplBrowserTest.DownloadImage_Deny_FileImage
- WebContentsImplBrowserTest.DownloadImage_Allow_FileImage

TBR=falken@chromium.org

No-Try: true
Bug: 1124349
Change-Id: I5412e0a932b22952e4243c7f075260bf2b434405
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2391889Reviewed-by: Makoto Shimazu <shimazu@chromium.org>
Commit-Queue: Makoto Shimazu <shimazu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804164}

content/browser/web_contents/web_contents_impl_browsertest.cc

@@ -2083,8 +2083,9 @@ IN_PROC_BROWSER_TEST_F(WebContentsImplBrowserTest,
   DownloadImageTestInternal(shell(), kImageUrl, 200, 1);
 }
 
+// Disabled due to flakiness: https://crbug.com/1124349.
 IN_PROC_BROWSER_TEST_F(WebContentsImplBrowserTest,
-                       DownloadImage_Deny_FileImage) {
+                       DISABLED_DownloadImage_Deny_FileImage) {
   ASSERT_TRUE(embedded_test_server()->Start());
   shell()->LoadURL(embedded_test_server()->GetURL("/simple_page.html"));
 
@@ -2092,8 +2093,9 @@ IN_PROC_BROWSER_TEST_F(WebContentsImplBrowserTest,
   DownloadImageTestInternal(shell(), kImageUrl, 0, 0);
 }
 
+// Disabled due to flakiness: https://crbug.com/1124349.
 IN_PROC_BROWSER_TEST_F(WebContentsImplBrowserTest,
-                       DownloadImage_Allow_FileImage) {
+                       DISABLED_DownloadImage_Allow_FileImage) {
   shell()->LoadURL(GetTestUrl("", "simple_page.html"));
 
   const GURL kImageUrl =