Add global opacity support to WebGL image replay

vectorLayer.setOpacity() now works as expected.

src/ol/renderer/webgl/webglmaprenderer.js

@@ -291,8 +291,9 @@ ol.renderer.webgl.Map.prototype.dispatchComposeEvent_ =
       var center = viewState.center;
       var rotation = viewState.rotation;
       var size = frameState.size;
+      var opacity = 1;
       replayGroup.replay(context, center, resolution, rotation, size, extent,
-          pixelRatio, {});
+          pixelRatio, opacity, {});
     }
     this.replayGroup = replayGroup;
   }

src/ol/renderer/webgl/webglvectorlayerrenderer.js

@@ -73,6 +73,7 @@ ol.renderer.webgl.VectorLayer.prototype.composeFrame =
     replayGroup.replay(context,
         viewState.center, viewState.resolution, viewState.rotation,
         frameState.size, frameState.extent, frameState.pixelRatio,
+        layerState.opacity,
         frameState.skippedFeatureUids);
   }