Take advantage of XDAMAGE to support Screen Capture under ChromeOS.

Screen Capture polls under Linux/X11, to avoid issues with poor XDAMAGE
support in some X hardware drivers for things like 3D rendering.

This CL enables XDAMAGE support under ChromeOS, since on that platform we
can make sure that the drivers support it properly.

BUG=177977


Review URL: https://chromiumcodereview.appspot.com/12408035

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@190032 0039d316-1c4b-4281-b951-d872f2087c98

media/video/capture/screen/screen_capture_device.cc

@@ -271,8 +271,15 @@ void ScreenCaptureDevice::Core::DoAllocate(int frame_rate) {
   frame_rate_ = frame_rate;
 
   // Create and start frame capturer.
+#if defined(OS_CHROMEOS)
+  // ScreenCapturerX11 polls by default, due to poor driver support for DAMAGE.
+  // ChromeOS' drivers [can be patched to] support DAMAGE properly, so use it.
+  if (!screen_capturer_)
+    screen_capturer_ = ScreenCapturer::CreateWithXDamage(true);
+#else
   if (!screen_capturer_)
     screen_capturer_ = ScreenCapturer::Create();
+#endif
   if (screen_capturer_)
     screen_capturer_->Start(this);