[Sheriff] Disable SaveAsMHTML on all slow bots

TBR=benwells@chromium.org

Bug: 1017305
Change-Id: If6820dc2e87850a5f3965a8bef663e5a0ff0c531
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1878908Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Commit-Queue: Stephen McGruer <smcgruer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709038}

chrome/browser/extensions/api/page_capture/page_capture_apitest.cc

@@ -76,8 +76,8 @@ class PageCaptureSaveAsMHTMLDelegate
 #endif
 
 // TODO(crbug.com/961017): Fix memory leaks in tests and re-enable on LSAN.
-// Also flaky-failing on Linux Tests (dbg): https://crbug.com/1017305
-#if defined(LEAK_SANITIZER) || (defined(OS_LINUX) && !defined(NDEBUG))
+// Also flaky-failing on slow (debug) bots: https://crbug.com/1017305
+#if defined(LEAK_SANITIZER) || !defined(NDEBUG)
 #define MAYBE_SaveAsMHTML DISABLED_SaveAsMHTML
 #else
 #define MAYBE_SaveAsMHTML SaveAsMHTML