Bug 1404749: Release our DrawTargetCapture on the main thread. r=mattwoodrow

MozReview-Commit-ID: 7uRdl2ZWtGS

gfx/layers/PaintThread.cpp

@@ -200,6 +200,13 @@ PaintThread::AsyncPaintContents(CompositorBridgeChild* aBridge,
   if (!mDrawTargetsToFlush.Contains(target)) {
     mDrawTargetsToFlush.AppendElement(target);
   }
+
+  if (gfxPrefs::LayersOMTPReleaseCaptureOnMainThread()) {
+    // This should ensure the capture drawtarget, which may hold on to UnscaledFont objects,
+    // gets destroyed on the main thread (See bug 1404742). This assumes (unflushed) target
+    // DrawTargets do not themselves hold on to UnscaledFonts.
+    NS_ReleaseOnMainThreadSystemGroup("CapturePaintState::DrawTargetCapture", aState->mCapture.forget());
+  }
 }
 
 void

gfx/thebes/gfxPrefs.h

@@ -619,6 +619,7 @@ private:
   DECL_GFX_PREF(Once, "layers.offmainthreadcomposition.force-disabled", LayersOffMainThreadCompositionForceDisabled, bool, false);
   DECL_GFX_PREF(Live, "layers.offmainthreadcomposition.frame-rate", LayersCompositionFrameRate, int32_t,-1);
   DECL_GFX_PREF(Live, "layers.omtp.force-sync",                LayersOMTPForceSync, bool, false);
+  DECL_GFX_PREF(Live, "layers.omtp.release-capture-on-main-thread", LayersOMTPReleaseCaptureOnMainThread, bool, true);
   DECL_GFX_PREF(Live, "layers.orientation.sync.timeout",       OrientationSyncMillis, uint32_t, (uint32_t)0);
   DECL_GFX_PREF(Once, "layers.prefer-opengl",                  LayersPreferOpenGL, bool, false);
   DECL_GFX_PREF(Live, "layers.progressive-paint",              ProgressivePaint, bool, false);

modules/libpref/init/all.js

@@ -5915,4 +5915,5 @@ pref("toolkit.crashreporter.include_context_heap", true);
 pref("dom.noopener.newprocess.enabled", true);
 
 pref("layers.omtp.enabled", false);
+pref("layers.omtp.release-capture-on-main-thread", true);
 pref("layers.omtp.force-sync", false);