Allow setting devicePixelRatio

[DeviaVir]

When qtwebkit/qtwebkit#515 is merged, the changes here will become valid and should allow users to overwrite the devicePixelRatio as first introduced in this PR:
#12839

The sample should still be valid:

var webPage = require('webpage');
var page = webPage.create();

// An example url that supports @2x background-image with the following css:-
/* body {
     background-image: background-image: url('http://retinajs.s3.amazonaws.com/images/backgrounds/bg.jpg');
  }
  @media all and (-webkit-min-device-pixel-ratio: 1.5) {
     body {
       background-image: background-image: url('http://retinajs.s3.amazonaws.com/images/backgrounds/bg@2x.jpg');
    }
} */
var examplePage = 'http://imulus.github.io/retinajs/';

//Pass a dpr of your choosing
page.devicePixelRatio = 1.5; // in this case, >=1.5 to get the retina-supporting bg-image

page.open(examplePage, function() {
   var backgroundImage = page.evaluate(function() {
     return window.getComputedStyle(document.body).backgroundImage;
   });
   console.log(backgroundImage); // returns http://retinajs.s3.amazonaws.com/images/backgrounds/bg@2x.jpg
   page.render('2x.png');
});

Fixes #10964

[ariya]

This definitely needs some tests.

[DeviaVir]

Tests results (with src/qt/qtwebkit on my branch):

$ python run-tests.py
ff....................f..........f...............s................ff.............s....f...
60.230s elapsed
  215 passed
   14 failed as expected
    2 skipped

cc: @ariya

[pholmstr]

Could be way off base here, but window.devicePixelRatio is a read only value so I wouldn't think it would be changeable via javascript. If the device supports high DPI then the devicePixelRatio should already be set.

Still waiting desperately for this feature 👍

[DeviaVir]

This now depends on qtwebkit/qtwebkit#515

[DeviaVir]

ping @ariya, I was hoping to get a pre-approval on this PR while we wait for qtwebkit/qtwebkit#515, is there anything I need to add or update about this PR?

[DeviaVir]

The related PR qtwebkit/qtwebkit#515 has been merged, there are no more blockers to merge this PR. @ariya who is best to ping to land this?

[DeviaVir]

@vitallium are you the right person to ping for this? I think this PR is cleared to merge.

[DeviaVir]

@ariya @vitallium apologies for pinging you in case you are no longer maintaining this: any ideas re: next steps for this PR?

[vitallium]

Landed in master!

[vitallium]

@DeviaVir also, I missed your PR and committed changes by myself. I do not want to take credits for that, send me please your Name and Email and I will alter the author of the commit to you. Sorry and thank you!

[CWBudde]

Does anyone have an idea when there will be a new release including this change? And when will it be added to the documentation?