Bug 1709900 - Do not call ScreenshotGrabber::MaybeGrabScreenshot() when RenderCompositorLayersSWGL::mCompositingStarted is false r=mstange,gfx-reviewers

mCompositor->BeginFrameForWindow() needs to be called for  ScreenshotGrabber::MaybeGrabScreenshot() with CompositorD3D11.

Differential Revision: https://phabricator.services.mozilla.com/D114714

gfx/webrender_bindings/RenderCompositorLayersSWGL.cpp

@@ -341,6 +341,9 @@ bool RenderCompositorLayersSWGL::MaybeRecordFrame(
 
 bool RenderCompositorLayersSWGL::MaybeGrabScreenshot(
     const gfx::IntSize& aWindowSize) {
+  if (!mCompositingStarted) {
+    return true;
+  }
   layers::WindowLMC window(mCompositor);
   mProfilerScreenshotGrabber.MaybeGrabScreenshot(window, aWindowSize);
   return true;