Prerequisites:
You'll need to have Unity Editor + WebGL support installed.

Steps to repro:

1. Open attached project and 't1' scene;
2. Open Profiler window (Window -> Profiler);
3. In the opened Profiler window click 'Profile Editor' button;
4. Open Rendering tab in Profiler window;
5. Observe that there are Batched Draw calls within '(Instancing)' section;
6. Open Build Settings window (File -> BuildSettings);
7. In the opened Build Settings window select 'WebGL' and click Switch platform;
8. Observe Batched Draw calls.

Expected result:
There should be batched (Instanced) draw calls for WebGL 2.0.

Actual result:
Draw calls are not batched with GPU Instancing (see attached video).

This outcome is inconsistent with other Graphics APIs supported by GPU Instancing. You may find that Instancing should be supported on WebGL 2.0 here: https://docs.unity3d.com/2017.2/Documentation/Manual/GPUInstancing.html

Notes:
- Reproducible on 2017.3.0b3, 2017.2.0f2, 2017.1.0f3;
- Reproducible only for WebGL platform; not reproducible for DX11;
- Reproducible in both Editor and Standalone player;
- GPU Instancing works on WebGL 2.0 if project was upgraded from older version with instanced shaders.