Prevent upscaling in desktop capture.

Prevent upscaling in desktop capture.

The previous CL landed (r238359) is missing a size check to prevent upscaling
in desktop capture. The correct logic should be to use native resolution
if both maxWidth and maxHeight are no smaller than source dimensions, and
to compute letterbox region if otherwise.

BUG=324923
TEST=trybot, Chrome OS feedback screen captures in native resolution
R=sergeyu@chromium.org
TBR=wjia@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=238514

[hshi1, 2013-12-03 23:54:39]

+sergeyu@ PTAL - sorry I have to re-open the bug because the CL I landed last
night was missing the very important logic to prevent upscaling.

The correct logic should be that we use native resolution if maxWidth/maxHeight
is no smaller than source dimentions, and use computeLetterboxRegion if maxWidth
or maxHeight is smaller than native resolution.

[Sergey Ulanov, 2013-12-04 01:08:32]

lgtm

[hshi1, 2013-12-04 01:12:26]

Committed patchset #1 manually as r238514 (presubmit successful).