Improve performance of FindFormControlElementsByUniqueRendererId

Before this CL, FindFormControlElementsByUniqueRendererId did many
linear searches over its vector parameter |form_control_renderer_ids|,
and accordingly had a DCHECK that the vector doesn't contain more than
10 elements.
This CL changes the implementation to build and use a map instead for
the lookups, thus avoiding the linear searches, and making
FindFormControlElementsByUniqueRendererId appropriate for larger
inputs.

Bug: 1004777
Change-Id: I0699d87de7202f42269c3504ecf08356ee880601
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1899455Reviewed-by: Vadym Doroshenko <dvadym@chromium.org>
Commit-Queue: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712552}

components/autofill/content/renderer/form_autofill_util.cc

@@ -2164,23 +2164,24 @@ WebFormControlElement FindFormControlElementsByUniqueRendererId(
 std::vector<WebFormControlElement> FindFormControlElementsByUniqueRendererId(
     WebDocument doc,
     const std::vector<uint32_t>& form_control_renderer_ids) {
-  DCHECK_LE(form_control_renderer_ids.size(), 10u)
-      << "More effective look-up should be implemented";
   WebElementCollection elements = doc.All();
   std::vector<WebFormControlElement> result(form_control_renderer_ids.size());
 
+  // Build a map from entries in |form_control_renderer_ids| to their indices,
+  // for more efficient lookup.
+  std::map<uint32_t, size_t> renderer_id_to_index;
+  for (size_t i = 0; i < form_control_renderer_ids.size(); i++)
+    renderer_id_to_index[form_control_renderer_ids[i]] = i;
+
   for (WebElement element = elements.FirstItem(); !element.IsNull();
        element = elements.NextItem()) {
     if (!element.IsFormControlElement())
       continue;
     WebFormControlElement control = element.To<WebFormControlElement>();
-    auto it = std::find(form_control_renderer_ids.begin(),
-                        form_control_renderer_ids.end(),
-                        control.UniqueRendererFormControlId());
-    if (it == form_control_renderer_ids.end())
+    auto it = renderer_id_to_index.find(control.UniqueRendererFormControlId());
+    if (it == renderer_id_to_index.end())
       continue;
-    size_t index = std::distance(form_control_renderer_ids.begin(), it);
-    result[index] = control;
+    result[it->second] = control;
   }
 
   return result;
@@ -2190,23 +2191,24 @@ std::vector<WebFormControlElement> FindFormControlElementsByUniqueRendererId(
     WebDocument doc,
     uint32_t form_renderer_id,
     const std::vector<uint32_t>& form_control_renderer_ids) {
-  DCHECK_LE(form_control_renderer_ids.size(), 10u)
-      << "More effective look-up should be implemented";
   std::vector<WebFormControlElement> result(form_control_renderer_ids.size());
   WebFormElement form = FindFormByUniqueRendererId(doc, form_renderer_id);
   if (form.IsNull())
     return result;
 
+  // Build a map from entries in |form_control_renderer_ids| to their indices,
+  // for more efficient lookup.
+  std::map<uint32_t, size_t> renderer_id_to_index;
+  for (size_t i = 0; i < form_control_renderer_ids.size(); i++)
+    renderer_id_to_index[form_control_renderer_ids[i]] = i;
+
   WebVector<WebFormControlElement> fields;
   form.GetFormControlElements(fields);
   for (const auto& field : fields) {
-    auto it = std::find(form_control_renderer_ids.begin(),
-                        form_control_renderer_ids.end(),
-                        field.UniqueRendererFormControlId());
-    if (it == form_control_renderer_ids.end())
+    auto it = renderer_id_to_index.find(field.UniqueRendererFormControlId());
+    if (it == renderer_id_to_index.end())
       continue;
-    size_t index = std::distance(form_control_renderer_ids.begin(), it);
-    result[index] = field;
+    result[it->second] = field;
   }
   return result;
 }

components/autofill/content/renderer/form_autofill_util.h

@@ -295,8 +295,6 @@ blink::WebFormControlElement FindFormControlElementsByUniqueRendererId(
 // Returns form control elements by unique renderer id. The result has the same
 // number elements as |form_control_renderer_ids| and i-th element of the result
 // corresponds to the i-th element of |form_control_renderer_ids|.
-// |form_control_renderer_ids| is supposed to be small (<=10 elements), because
-// it is being frequently searched by linear pass over its elements.
 // The call of this function might be time expensive, because it retrieves all
 // DOM elements.
 std::vector<blink::WebFormControlElement>
@@ -308,8 +306,6 @@ FindFormControlElementsByUniqueRendererId(
 // id |form_renderer_id|. The result has the same number elements as
 // |form_control_renderer_ids| and i-th element of the result corresponds to the
 // i-th element of |form_control_renderer_ids|.
-// |form_control_renderer_ids| is supposed to be small (<=10 elements), because
-// it is being frequently searched by linear pass over its elements.
 // This function is faster than the previous one, because it only retrieves form
 // control elements from a single form.
 std::vector<blink::WebFormControlElement>