[Window Capturer] Inaccurate cursor position on cinnamon
[Window Capturer] Inaccurate cursor position on cinnamon

When cinnamon is used, it always wraps the application window with its own
window. Instead of (0, 0), the DesktopRect from XWindowAttributes starts from
(10, 36).
So this change considers this difference when translating the DesktopRect in
GetWindowRect() function.

Bug: chromium:778035
Change-Id: I4944b2d1e13a4c379e114fd1749d74e95a63003b
Reviewed-on: https://webrtc-review.googlesource.com/17660
Reviewed-by: Jamie Walch <6969cd2a405898dc33bef14ddd3e152c3cd07803@chromium.org>
Commit-Queue: Zijie He <0175c16456617950f1607b27294c14b126a588d1@chromium.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#20538}
ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc