Disabling BasicDesktopEnvironment::CreateComposingVideoCapturer for M81

The plan is to submit this change and merge it to M81 to address
multi-mon issues in that release.  Once Jamie is back, he will revert
this change and finish the VideoCapturer impl for M82.

Change-Id: I33f1261061c43afeffbfc76df138440daa56f80e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2048306
Auto-Submit: Joe Downing <joedow@chromium.org>
Reviewed-by: Jamie Walch <jamiewalch@chromium.org>
Commit-Queue: Joe Downing <joedow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#740318}

remoting/host/basic_desktop_environment.cc

@@ -100,8 +100,11 @@ BasicDesktopEnvironment::CreateComposingVideoCapturer() {
   // MacOS always includes the mouse cursor in the captured image.
   return nullptr;
 #else
-  return std::make_unique<DesktopAndCursorConditionalComposer>(
-      CreateVideoCapturer());
+  // TODO(crbug.com/1050789): Return a valid instance after fixing the
+  // DesktopAndCursorConditionalComposer class.
+  // return std::make_unique<DesktopAndCursorConditionalComposer>(
+  //     CreateVideoCapturer());
+  return nullptr;
 #endif
 }