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

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

With present implementation autofill/autocomplete suggestions are matched for
prefix for what user has typed.

This patch brings in suggestions with substring matching (i.e. substring matching
to the beginning of suggestion tokens) instead of prefix matching.

Patch spread across chromium side as well as on Blink side.
[1] Blink side: https://codereview.chromium.org/1208063002/
    - aims to cache the suggestion start index with |WebFormControlElement| so that
      chromium content can make use of it on setting selection range.
[2] Chromium side: https://codereview.chromium.org/1208133002/ (This CL)
    - aims to add IPC changes to introduce |match_start| for suggestion preview in
      case of password manager and autocomplete so that additional calulation on
      renderer to get selection range in not needed.
[3] Chromium side: https://codereview.chromium.org/962673004/
    - Substring match instead of prefixes.

BUG=77194

[Pritam Nikam, 2015-06-25 17:39:28]

pritam.nikam@samsung.com changed reviewers:
+ rouslan@chromium.org

[Pritam Nikam, 2015-06-25 17:44:31]

Hi Rouslan,

I've added this patch just to get a fair idea on IPC side changes alone. this
involved introduction of |match_start| in suggestion that is where we will be
keeping calculation of start offset of user input to that of suugestion string.
Same being passed over wire to the rendender so that we dont have to calculate
it again on setiing the text selection range in form input field. Please have a
look and help me with your inputs.

Thanks!

[Pritam Nikam, 2015-06-26 13:58:00]

On 2015/06/25 17:44:31, Pritam Nikam wrote:
> Hi Rouslan,
> 
> I've added this patch just to get a fair idea on IPC side changes alone. this
> involved introduction of |match_start| in suggestion that is where we will be
> keeping calculation of start offset of user input to that of suugestion
string.
> Same being passed over wire to the rendender so that we dont have to calculate
> it again on setiing the text selection range in form input field. Please have
a
> look and help me with your inputs.
> 
> Thanks!

Hi Rouslan,

I've modified this patch with few more excerpts, as mentioned in [1] its working
for me on my local setup currenly with below exceprt in
|PasswordAutofillAgent::PreviewSuggestion| and
|AutofillAgent::PreviewFieldWithValue| for prefix match and passing
|match_start| without requiring Blink changes.

node->setSelectionRange(std::min(match_start, node->maxLength()),
                        node->suggestedValue().length());

[1] https://codereview.chromium.org/1208063002/#msg4

Thanks!

[please use gerrit instead, 2015-06-28 00:45:12]

After reviewing this patch, I agree with your first assessment that this patch
is not necessary. Let's continue review in your original patch. I've posted a
few comments there already.