Revert "Disable subpixel positioning on chrome os"

This reverts commit e3cf0f78.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> Disable subpixel positioning on chrome os
> 
> Subpixel positioning was needed because text layout was performed at 1x
> device scale factor and then rastered to the final display device scale
> factor leading to glyph artifacts and inconsistent glyph positioning.
> With pixel canvas enabled on chrome os, the text layout is now always
> performed at the final display device scale factor. This, coupled with
> the replacement of ui scale with display zoom, the text on Chrome OS
> is now always rastered with the correct glyph positioning and it no
> longer requires subpixel positioning.
> 
> Bug:835187,824154,716662
> Change-Id: Idc0d6c7851308cc26b1d90f74a619e90dadf0112
> Component: Text render, subpixel positioning, font
> 
> TBR=derat@chromium.org
> 
> Change-Id: Idc0d6c7851308cc26b1d90f74a619e90dadf0112
> Reviewed-on: https://chromium-review.googlesource.com/1026636
> Reviewed-by: Malay Keshav <malaykeshav@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#553353}

TBR=derat@chromium.org,malaykeshav@chromium.org

Change-Id: I22601786db33c0082480a09e9e7a3905a56a1383
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 835187, 824154, 716662
Reviewed-on: https://chromium-review.googlesource.com/1026438Reviewed-by: Malay Keshav <malaykeshav@chromium.org>
Commit-Queue: Malay Keshav <malaykeshav@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553392}

ui/gfx/font_render_params_linux.cc

@@ -278,14 +278,12 @@ FontRenderParams GetFontRenderParams(const FontRenderParamsQuery& query,
     params.hinting = FontRenderParams::HINTING_FULL;
     params.subpixel_rendering = FontRenderParams::SUBPIXEL_RENDERING_NONE;
     params.subpixel_positioning = false;
-#if !defined(OS_CHROMEOS)
   } else {
     params.subpixel_positioning = actual_query.device_scale_factor > 1.0f;
 
     // To enable subpixel positioning, we need to disable hinting.
     if (params.subpixel_positioning)
       params.hinting = FontRenderParams::HINTING_NONE;
-#endif  //  !defined(OS_CHROMEOS)
   }
 
   // Use the first family from the list if Fontconfig didn't suggest a family.