UserAgent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.84 Safari/537.36

Steps to reproduce the problem:
1. Enter data in a form and submit the page.
2. Return to the previous page (the one with the form). Your previously entered data should be pre-filled.
3. Correct the data in a field other than address line 1.
4. Observe that the updated data has not been added to your autofill profiles.

What is the expected behavior?
Despite the desired effect of not saving placeholder data to a profile, this also causes autofill to not recognize partial updates to data. (Ex. updating the zip code on your profile page where your previously saved data has been filled by the website). It would be good to implement heuristics to differentiate fake placeholder data from pre-filled user data.

What went wrong?
Upon form submit, the form will be validated (AutofillManager::ValidateSubmittedForm) during which FormStructure::UpdateFromCache is run. This compares the current state of the FormStructure with a cached version. Generally this cached version is the one created when the field types are detected on page load. If this function finds that a non-select type field has been submitted with a value matching the cached version then it's value is set to an empty string.

The effect of this is that the resultant form structure will only contain the modified data. However, this means that the changes made might get lost if the minimum required data (checked in PersonalDataManager::IsValidLearnableProfile)(ex. address line 1) is included in the changed data. Even then, other existing data might get lost.

Did this work before? N/A 

Chrome version: 51.0.2704.84  Channel: n/a
OS Version: Ubuntu 14.04
Flash Version: Shockwave Flash 21.0 r0