Account for DIP when setting the preferred size for tab capture.

Account for DIP when setting the preferred size for tab capture.

This is an optimization for systems where there is more than one
physical pixel per logical pixel (e.g., Chromebook Pixel, Mac Retina).
On these systems, the render widget should be "preferably" sized such
that its physical size will match that of the tab capture frame size.

Because the entire graphics pipeline is handling N^2 less data, and also
will no longer need to down-scale images, users should see huge tab
capture performance improvements (e.g., higher frame rates, lower CPU
utilization and fan noise).

Expected side effect: Fullscreen-Within-Tab widgets will appear shrunk.
However, since content renderers are still DIP-aware, any UI controls
within the widget will appear right-sized.  In other words, user
interaction will not be diminished by this change.

Testing: Confirmed Fullscreen-Within-Tab and tab capture output is
correct by varying --force-device-scale-factor=X.

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=289040

[miu, 2014-08-11 00:13:01]

hclam: PTAL.

[Alpha Left Google, 2014-08-11 17:25:57]

lgtm

[commit-bot: I haz the power, 2014-08-11 17:26:57]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/miu@chromium.org/461443003/1

[commit-bot: I haz the power, 2014-08-12 00:57:10]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  linux_chromium_chromeos_rel_swarming on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  linux_chromium_rel_swarming on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  win_chromium_rel on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel/...)
  win_chromium_x64_rel on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_...)

[commit-bot: I haz the power, 2014-08-12 01:43:40]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-08-12 01:43:44]

Try jobs failed on following builders:
  linux_chromium_chromeos_rel_swarming on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  linux_chromium_rel_swarming on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[miu, 2014-08-12 03:32:51]

The CQ bit was checked by miu@chromium.org

[commit-bot: I haz the power, 2014-08-12 03:34:41]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/miu@chromium.org/461443003/20001

[commit-bot: I haz the power, 2014-08-12 07:36:15]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_chromium_x64_rel on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_...)

[commit-bot: I haz the power, 2014-08-12 10:18:56]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-08-12 10:18:58]

Try jobs failed on following builders:
  win_chromium_x64_rel on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_...)

[miu, 2014-08-12 16:34:42]

The CQ bit was checked by miu@chromium.org

[commit-bot: I haz the power, 2014-08-12 16:36:51]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/miu@chromium.org/461443003/20001

[commit-bot: I haz the power, 2014-08-12 18:50:46]

Change committed as 289040