[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(),

[Evan Stade, 2015/03/31 21:41:52]

can you use StartsAt directly

[Pritam Nikam, 2015/04/01 09:10:37]

StartsAt() is not equipped handle all complected cases.

for eg. 
1. field_suggestion = L"ba.a.ab"  and field_contents = L"a.a"
   
   After executing ComputeRange() ->
   offset = 3, start = 6 & end = 7.

2. field_suggestion = L"texample@example.com" and field_contents = L"example"

   After executing ComputeRange() ->
   offset = 9, start = 16 & end = 20.

IMO StartsAt() shall handle only basic case i.e. to return the first occurrence
offset of search string. And ComputeRange() shall use it to get actual data
(i.e. selection start and end indexes) that we are interested in.

I've modified ComputeRange() to meet these these cases.

+                                 &start, &end)) {
+        field->setSelectionRange(start, end);
+      }
+    } else {
+      field->setSelectionRange(field->value().length(),
+                               field->suggestedValue().length());
+    }
   }
 }