Make FindTaskController::FindTask::Invoke() to avoid to use invalid range

Because we don't have sample HTML to cause this case but we see crash
logs, thiis a speculative patch to avoid crash caused by attempting
to construct invalid range in |FindTaskController::FindTask::
Invoke()|.

Bug: 1125953
Change-Id: I38d43bf6e66e44ba25529aa8a2dffea5523a49eb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2413460
Auto-Submit: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#807377}

third_party/blink/renderer/core/editing/finder/find_task_controller.cc

@@ -108,7 +108,7 @@ class FindTaskController::FindTask final : public GarbageCollected<FindTask> {
         (options_->new_session ? kStartInSelection : 0);
     auto start_time = base::TimeTicks::Now();
 
-    while (search_start != search_end) {
+    while (search_start < search_end) {
       // Find in the whole block.
       FindBuffer buffer(EphemeralRangeInFlatTree(search_start, search_end));
       FindBuffer::Results match_results =