[Autofill/Autocomplete Feature] Substring matching instead of prefix matching.

components/autofill/content/renderer/autofill_agent.cc

Index: components/autofill/content/renderer/autofill_agent.cc
diff --git a/components/autofill/content/renderer/autofill_agent.cc b/components/autofill/content/renderer/autofill_agent.cc
index 79542aff2520a500debcf60c29699d73e28d5524..36fb679e0e0d7f4b48048d9468aad4c26c9580f7 100644
--- a/components/autofill/content/renderer/autofill_agent.cc
+++ b/components/autofill/content/renderer/autofill_agent.cc
@@ -571,10 +571,11 @@ void AutofillAgent::OnFillFieldWithValue(const base::string16& value) {
   }
 }
 
-void AutofillAgent::OnPreviewFieldWithValue(const base::string16& value) {
+void AutofillAgent::OnPreviewFieldWithValue(const base::string16& value,
+                                            int match_start) {
   WebInputElement* input_element = toWebInputElement(&element_);
   if (input_element)
-    PreviewFieldWithValue(value, input_element);
+    PreviewFieldWithValue(value, input_element, match_start);
 }
 
 void AutofillAgent::OnAcceptDataListSuggestion(const base::string16& value) {
@@ -590,13 +591,11 @@ void AutofillAgent::OnFillPasswordSuggestion(const base::string16& username,
   DCHECK(handled);
 }
 
-void AutofillAgent::OnPreviewPasswordSuggestion(
-    const base::string16& username,
-    const base::string16& password) {
-  bool handled = password_autofill_agent_->PreviewSuggestion(
-      element_,
-      username,
-      password);
+void AutofillAgent::OnPreviewPasswordSuggestion(const base::string16& username,
+                                                const base::string16& password,
+                                                int start) {
+  bool handled = password_autofill_agent_->PreviewSuggestion(element_, username,
+                                                             password, start);
   DCHECK(handled);
 }
 
@@ -736,11 +735,12 @@ void AutofillAgent::FillFieldWithValue(const base::string16& value,
 }
 
 void AutofillAgent::PreviewFieldWithValue(const base::string16& value,
-                                          WebInputElement* node) {
+                                          WebInputElement* node,
+                                          int match_start) {
   was_query_node_autofilled_ = element_.isAutofilled();
   node->setSuggestedValue(value.substr(0, node->maxLength()));
   node->setAutofilled(true);
-  node->setSelectionRange(node->value().length(),
+  node->setSelectionRange(std::min(match_start, node->maxLength()),
                           node->suggestedValue().length());
 }