Apply the layer's image filter to the hoisted image

Exposing SkSurface_Gpu makes me sad and I would welcome alternatives.

This change is desireable since it greatly decreases the render target swaps.

Review URL: https://codereview.chromium.org/792923002
diff --git a/gyp/gpu.gyp b/gyp/gpu.gyp
index 6319456..e835e34 100644
--- a/gyp/gpu.gyp
+++ b/gyp/gpu.gyp
@@ -96,6 +96,7 @@
         '../include/gpu',
         '../src/core',
         '../src/gpu',
+        '../src/image/',
       ],
       'sources': [
         '<@(skgpu_sources)',