Fix multipicturedraw_biglayer GM

Having a layer is a prerequisite for having it be hoisted.

Review URL: https://codereview.chromium.org/632743002
diff --git a/gm/multipicturedraw.cpp b/gm/multipicturedraw.cpp
index afa83e5..8ce3deb 100644
--- a/gm/multipicturedraw.cpp
+++ b/gm/multipicturedraw.cpp
@@ -106,6 +106,8 @@
     static const SkScalar kBig = 10000.0f;
     SkCanvas* canvas = recorder.beginRecording(kBig, kBig);
 
+    canvas->saveLayer(NULL, NULL);
+
     SkScalar xPos = 0.0f, yPos = 0.0f;
 
     for (int y = 0; yPos < kBig; ++y) {
@@ -127,6 +129,8 @@
         yPos += 2 * kHexSide * kRoot3Over2;
     }
 
+    canvas->restore();
+
     return recorder.endRecording();
 }