This change is to add an DesktopCapturerOptions accurate_updated_region() with
default value as false to indicate whether a pixel-wise differentiation is
required. And ScreenCapturer::Create() function will wrap the implementation
with ScreenCapturerDifferWrapper.
Chromoting will use this option to filter out unchanged frames.
BUG=314516
Review-Url: https://codereview.webrtc.org/2314323002
Cr-Commit-Position: refs/heads/master@{#14248}