skia: add ability to load command_buffer_gles2

BUG=skia:

Review URL: https://codereview.chromium.org/1306823003
diff --git a/tools/PictureRenderer.cpp b/tools/PictureRenderer.cpp
index 700d3d3..c491e86 100644
--- a/tools/PictureRenderer.cpp
+++ b/tools/PictureRenderer.cpp
@@ -139,6 +139,10 @@
         case kAngle_DeviceType:
             // fall through
 #endif
+#if SK_COMMAND_BUFFER
+        case kCommandBuffer_DeviceType:
+            // fall through
+#endif
 #if SK_MESA
         case kMesa_DeviceType:
             // fall through