Bug 1603207 - Only enable native compositor if picture caching enabled. r=sotaro

Differential Revision: https://phabricator.services.mozilla.com/D56817

--HG--
extra : moz-landing-system : lando

gfx/webrender_bindings/RenderCompositorANGLE.cpp

@@ -724,7 +724,8 @@ bool RenderCompositorANGLE::IsContextLost() {
 }
 
 bool RenderCompositorANGLE::UseCompositor() {
-  if (!mDCLayerTree || !gfx::gfxVars::UseWebRenderCompositor()) {
+  if (!mDCLayerTree || !gfx::gfxVars::UseWebRenderCompositor() ||
+      !StaticPrefs::gfx_webrender_picture_caching()) {
     return false;
   }
   return true;

gfx/webrender_bindings/RenderCompositorOGL.cpp

@@ -153,7 +153,8 @@ LayoutDeviceIntSize RenderCompositorOGL::GetBufferSize() {
 }
 
 bool RenderCompositorOGL::ShouldUseNativeCompositor() {
-  return mNativeLayerRoot && gfx::gfxVars::UseWebRenderCompositor();
+  return mNativeLayerRoot && gfx::gfxVars::UseWebRenderCompositor() &&
+         StaticPrefs::gfx_webrender_picture_caching();
 }
 
 uint32_t RenderCompositorOGL::GetMaxUpdateRects() {