Assert both display and system keep-alive on each capture.

media/video/capture/screen/screen_capturer_win.cc

Index: media/video/capture/screen/screen_capturer_win.cc
diff --git a/media/video/capture/screen/screen_capturer_win.cc b/media/video/capture/screen/screen_capturer_win.cc
index 796af5f85ea86b648598767a10e3fb9ef8914cdb..219641ecde45b5cfc63a2483ce907ef765b6e8aa 100644
--- a/media/video/capture/screen/screen_capturer_win.cc
+++ b/media/video/capture/screen/screen_capturer_win.cc
@@ -216,8 +216,10 @@ void ScreenCapturerWin::InvalidateRegion(const SkRegion& invalid_region) {
 void ScreenCapturerWin::CaptureFrame() {
   base::Time capture_start_time = base::Time::Now();
 
-  // Force the system to power-up display hardware, if it has been suspended.
-  SetThreadExecutionState(ES_DISPLAY_REQUIRED);
+  // Request that the system not power-down the system, or the display hardware.
+  if (!SetThreadExecutionState(ES_DISPLAY_REQUIRED | ES_SYSTEM_REQUIRED)) {
+    LOG(WARNING) << "Failed to make system & display power assertion";

[alexeypa (please no reviews), 2013/02/11 17:02:28]

nit #1: LOG_GETLASTERROR(WARNING).

nit #2: this will flood the log if SetThreadExecutionState() fails all the time.
Add some rate limiting logic. For instance do not log the _same_ error unless X
seconds passed since the last one. 

[Wez, 2013/02/12 01:52:46]

I've settled on just logging the first failure per capturer, which should be
enough for the main debug value of determining why the user's machine fell
asleep. :)

+  }
 
   // Make sure the GDI capture resources are up-to-date.
   PrepareCaptureResources();