[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 ee1ddd2970ef00e42208fa5675e9996f44bf9398..a8b3f31692f48ecfe6dab41b32b11b09f81d6480 100644
--- a/components/autofill/content/renderer/autofill_agent.cc
+++ b/components/autofill/content/renderer/autofill_agent.cc
@@ -19,6 +19,7 @@
 #include "components/autofill/core/common/autofill_constants.h"
 #include "components/autofill/core/common/autofill_data_validation.h"
 #include "components/autofill/core/common/autofill_switches.h"
+#include "components/autofill/core/common/autofill_util.h"
 #include "components/autofill/core/common/form_data.h"
 #include "components/autofill/core/common/form_data_predictions.h"
 #include "components/autofill/core/common/form_field_data.h"
@@ -765,8 +766,18 @@ void AutofillAgent::PreviewFieldWithValue(const base::string16& value,
   was_query_node_autofilled_ = element_.isAutofilled();
   node->setSuggestedValue(value.substr(0, node->maxLength()));
   node->setAutofilled(true);
-  node->setSelectionRange(node->value().length(),
-                          node->suggestedValue().length());
+
+  if (IsFeatureSubstringMatchEnabled()) {
+    size_t start = 0;
+    size_t end = 0;
+    if (base::string16::npos !=
+        ComputeRange(value, node->value(), &start, &end)) {
+      node->setSelectionRange(start, end);
+    }
+  } else {
+    node->setSelectionRange(node->value().length(),
+                            node->suggestedValue().length());
+  }
 }
 
 void AutofillAgent::ProcessForms() {