[Autofill Assistant] WaitForDomProto inconsistent.

Before this patch, the client and server protos differed in the fields ids and the
structure of the element to wait for. This resulted in selectors being empty and
timeout values off.

This patch fixes the numbering and replaces the element field with a
repeated string field.

After this patch, WaitForDomProto messages can properly be parsed.

Props to szermatt@ for finding this difference.

R=rouslan@chromium.org

Bug: 806868
Change-Id: Ib2c9822c6ef24001706b78c339f3d4b97c3aa947
Reviewed-on: https://chromium-review.googlesource.com/1249274
Commit-Queue: Mathias Carlen <mcarlen@chromium.org>
Reviewed-by: Rouslan Solomakhin <rouslan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595021}

components/autofill_assistant/browser/actions/wait_for_dom_action.cc

@@ -32,8 +32,8 @@ void WaitForDomAction::ProcessAction(ActionDelegate* delegate,
                                      ProcessActionCallback callback) {
   processed_action_proto_ = std::make_unique<ProcessedActionProto>();
 
-  // Fail the action if the selector is empty.
-  if (proto_.wait_for_dom().element().selectors().empty()) {
+  // Fail the action if selectors is empty.
+  if (proto_.wait_for_dom().selectors().empty()) {
     UpdateProcessedAction(false);
     DLOG(ERROR) << "Empty selector, failing action.";
     std::move(callback).Run(std::move(processed_action_proto_));
@@ -54,7 +54,7 @@ void WaitForDomAction::CheckElementExists(ActionDelegate* delegate,
                                           ProcessActionCallback callback) {
   DCHECK(rounds > 0);
   std::vector<std::string> selectors;
-  for (const auto& selector : proto_.wait_for_dom().element().selectors()) {
+  for (const auto& selector : proto_.wait_for_dom().selectors()) {
     selectors.emplace_back(selector);
   }
   delegate->ElementExists(

components/autofill_assistant/browser/service.proto

@@ -340,11 +340,11 @@ message UseCreditCardProto {
 // Ask Chrome to wait for an element in the DOM. This can be used to only
 // proceed to the next action once the page is ready.
 message WaitForDomProto {
-  // The element to wait.
-  optional ElementReferenceProto element = 1;
-
   // Fail after waiting this amount of time.
-  optional int32 timeout_ms = 2;
+  optional int32 timeout_ms = 1;
+
+  // The element to wait for.
+  repeated string selectors = 2;
 }
 
 // Volatile upload of a portion of the dom for backend analysis, does not store