Revert "Allow arbitrary scale factors."

Revert "Allow arbitrary scale factors."

Reason for revert: crbug.ccom/484400

BUG=143619, 484400
TBR=erg@chromium.org, estade@chromium.org, oshima@chromium.org, stapelberg@google.com

> Allow arbitrary scale factors.
>
>    As discussed in https://codereview.chromium.org/1070433002/, this CL
>    allows arbitrary scale factors, which works because chromium uses the
>    resource most closely matching the scale factor (e.g. 1x for 1.25x,
>    but 2x for 1.9x) and scales it.
>
>    BUG=143619, 477716
>
>    Review URL: https://codereview.chromium.org/1078423002
>
>    Cr-Commit-Position: refs/heads/master@{#326851}
>    (cherry picked from commit b3ca230ddd7d1238ee96ed26ea23e369f10dd655)
>
>    device scale factor detection: use gtk-xft-dpi consistently
>
>    Before this CL, we used either gtk-xft-dpi (UI fonts) or the physical DPI of
>    a more or less random display. This CL consistently uses gtk-xft-dpi which
>    is the better alternative: users can directly influence it (by changing the
>    Xft.dpi X resource, or via their gtkrc).
>
>    See also https://github.com/derat/font-config-info for displaying your
>    current system settings.
>
>    This is a re-do of https://codereview.chromium.org/1070433002/, but with
>    https://codereview.chromium.org/1084453002/ applied (fixes content_shell).
>
>    BUG=473089, 143619
>
>    Review URL: https://codereview.chromium.org/1085603002
>
>    Cr-Commit-Position: refs/heads/master@{#324928}
>    (cherry picked from commit d459a5c49a02507b9ac77ffbbf33dffeb3bc9c34)
>
>    R=stapelberg@google.com
>    TBR=erg, estade, oshima
>
>    Review URL: https://codereview.chromium.org/1103383004
>
>    Cr-Commit-Position: refs/branch-heads/2357@{#246}
>    Cr-Branched-From: 59d4494849b405682265ed5d3f5164573b9a939b-refs/heads/master@{#323860}

Committed: https://chromium.googlesource.com/chromium/src/+/1e83acd552618ab337d286187ed23d84434bd122

[oshima, 2015-05-26 20:49:13]

Committed patchset #1 (id:1) manually as
1e83acd552618ab337d286187ed23d84434bd122 (presubmit successful).