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

components/autofill/content/renderer/form_autofill_util.cc

Index: components/autofill/content/renderer/form_autofill_util.cc
diff --git a/components/autofill/content/renderer/form_autofill_util.cc b/components/autofill/content/renderer/form_autofill_util.cc
index 91d3572bc0d4df6142aa02620786d77109b8b78e..a180071e6cb4bf1b153eb031288c05028575f342 100644
--- a/components/autofill/content/renderer/form_autofill_util.cc
+++ b/components/autofill/content/renderer/form_autofill_util.cc
@@ -15,6 +15,7 @@
 #include "base/strings/utf_string_conversions.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_field_data.h"
 #include "third_party/WebKit/public/platform/WebString.h"
@@ -882,9 +883,18 @@ void PreviewFormField(const FormFieldData& data,
   if (is_initiating_node &&
       (IsTextInput(input_element) || IsTextAreaElement(*field))) {
     // Select the part of the text that the user didn't type.
-    int start = field->value().length();
-    int end = field->suggestedValue().length();
-    field->setSelectionRange(start, end);
+    if (IsFeatureSubstringMatchEnabled()) {
+      size_t start = 0;
+      size_t end = 0;
+      if (base::string16::npos !=
+          autofill::ComputeRange(field->suggestedValue(), field->value(),
+                                 &start, &end)) {
+        field->setSelectionRange(start, end);
+      }
+    } else {
+      field->setSelectionRange(field->value().length(),
+                               field->suggestedValue().length());
+    }
   }
 }