[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 51a2251258b73d0faf6bf61afbc8fec36b951d11..4cf695ffc3ec9b9e8f1b6a755c3b59dd037ab25e 100644
--- a/components/autofill/content/renderer/form_autofill_util.cc
+++ b/components/autofill/content/renderer/form_autofill_util.cc
@@ -16,6 +16,7 @@
 #include "components/autofill/core/common/autofill_data_validation.h"
 #include "components/autofill/core/common/autofill_regexes.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"
@@ -871,9 +872,7 @@ 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);
+    PreviewSuggestion(field->suggestedValue(), field->value(), field);
   }
 }
 
@@ -1534,4 +1533,19 @@ gfx::RectF GetScaledBoundingBox(float scale, WebElement* element) {
                     bounding_box.height() * scale);
 }
 
+void PreviewSuggestion(const base::string16& suggestion,
+                       const base::string16& user_input,
+                       blink::WebFormControlElement* input_element) {
+  size_t selection_start = user_input.length();
+  if (IsFeatureSubstringMatchEnabled()) {
+    size_t offset =
+        autofill::GetTextSelectionStart(suggestion, user_input, false);
+    // Zero selection start is for password manager, which can show usernames
+    // that do not begin with the user input value.
+    selection_start = (offset == base::string16::npos) ? 0 : offset;
+  }
+
+  input_element->setSelectionRange(selection_start, suggestion.length());
+}
+
 }  // namespace autofill