Bug 1292326 - Let layers.acceleration.force-enabled apply to the OPENGL_COMPOSITING feature. r=jrmuizel

MozReview-Commit-ID: 2Lx4CVOao6S

--HG--
extra : rebase_source : b7d3ff19ab2e219ac78a681d7a7785f2f6b57abe

gfx/thebes/gfxPlatform.cpp

@@ -2505,6 +2505,12 @@ gfxPlatform::InitOpenGLConfig()
   if (!IsGfxInfoStatusOkay(nsIGfxInfo::FEATURE_OPENGL_LAYERS, &message, failureId)) {
     openGLFeature.Disable(FeatureStatus::Blacklisted, message.get(), failureId);
   }
+
+  // Ensure that an accelerated compositor backend is available when layers
+  // acceleration is force-enabled.
+  if (gfxPrefs::LayersAccelerationForceEnabledDoNotUseDirectly()) {
+    openGLFeature.UserForceEnable("Force-enabled by pref");
+  }
 }
 
 bool