[Autofill Assistant] Fix WaitForDomAction.

Before this patch, WaitForDomAction could get into situation where
rounds was < 0 and crash in debug mode. This could happen if timeout_ms
was very small or at the end, if the element was not found.

This patch fixes the round counting and dchecks.

With this patch, WaitForDomAction won't crash in debug mode when the
element cannot be found.

Bug: 806868
Change-Id: I308883441876df66225550b9ddc43d1894a48de6
Reviewed-on: https://chromium-review.googlesource.com/c/1264576Reviewed-by: Ganggui Tang <gogerald@chromium.org>
Commit-Queue: Ganggui Tang <gogerald@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597160}

components/autofill_assistant/browser/actions/wait_for_dom_action.cc

@@ -4,6 +4,7 @@
 
 #include "components/autofill_assistant/browser/actions/wait_for_dom_action.h"
 
+#include <algorithm>
 #include <cmath>
 
 #include "base/bind.h"
@@ -44,7 +45,9 @@ void WaitForDomAction::ProcessAction(ActionDelegate* delegate,
 
   int timeout_ms = proto_.wait_for_dom().timeout_ms();
   if (timeout_ms > 0)
-    check_rounds = std::ceil(timeout_ms / kCheckPeriodInMilliseconds);
+    check_rounds = std::min(
+        1,
+        static_cast<int>(std::ceil(timeout_ms / kCheckPeriodInMilliseconds)));
 
   CheckElementExists(delegate, check_rounds, std::move(callback));
 }
@@ -52,7 +55,7 @@ void WaitForDomAction::ProcessAction(ActionDelegate* delegate,
 void WaitForDomAction::CheckElementExists(ActionDelegate* delegate,
                                           int rounds,
                                           ProcessActionCallback callback) {
-  DCHECK(rounds > 0);
+  DCHECK_GT(rounds, 0);
   std::vector<std::string> selectors;
   for (const auto& selector : proto_.wait_for_dom().selectors()) {
     selectors.emplace_back(selector);
@@ -73,13 +76,14 @@ void WaitForDomAction::OnCheckElementExists(ActionDelegate* delegate,
     return;
   }
 
-  if (rounds == 0) {
+  --rounds;
+  if (rounds <= 0) {
+    DCHECK_EQ(rounds, 0);
     UpdateProcessedAction(ELEMENT_RESOLUTION_FAILED);
     std::move(callback).Run(std::move(processed_action_proto_));
     return;
   }
 
-  --rounds;
   base::PostDelayedTaskWithTraits(
       FROM_HERE, {content::BrowserThread::UI},
       base::BindOnce(&WaitForDomAction::CheckElementExists,