Revert "Fix WebGL PushFrame crash when GetDrawingBuffer returns NULL"

This reverts commit 3b813a2b.

Reason for revert: <This is the suspected CL that breaks 12 GPU FYI bots on webgl2_conformance_validating_tests, webgl2_conformance_gl_passthrough_tests, webgl2_conformance_tests, webgl_conformance_d3d9_passthrough_tests and webgl_conformance_vulkan_passthrough_tests. Will come back to check the FYI results to decide if reland is needed.>

Original change's description:
> Fix WebGL PushFrame crash when GetDrawingBuffer returns NULL
> 
> Bug: 1059491
> Change-Id: I6df4870cb8ece3986a2ad0fecd28b50593ae2e8f
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2108874
> Reviewed-by: Kai Ninomiya <kainino@chromium.org>
> Reviewed-by: Kenneth Russell <kbr@chromium.org>
> Commit-Queue: Shrek Shao <shrekshao@google.com>
> Cr-Commit-Position: refs/heads/master@{#751547}

TBR=kbr@chromium.org,kainino@chromium.org,shrekshao@google.com

Change-Id: I1b88f2e4f36b69c6a4daf07d0fc4ee21830ebe1c
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1059491
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2109460Reviewed-by: Maggie Chen <magchen@chromium.org>
Commit-Queue: Maggie Chen <magchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#751623}

third_party/blink/renderer/modules/webgl/webgl_rendering_context_base.cc

@@ -1412,11 +1412,11 @@ void WebGLRenderingContextBase::DidDraw() {
 }
 
 bool WebGLRenderingContextBase::PushFrame() {
+  int width = GetDrawingBuffer()->Size().Width();
+  int height = GetDrawingBuffer()->Size().Height();
   int submitted_frame = false;
   if (PaintRenderingResultsToCanvas(kBackBuffer)) {
     if (Host()->GetOrCreateCanvasResourceProvider(kPreferAcceleration)) {
-      int width = GetDrawingBuffer()->Size().Width();
-      int height = GetDrawingBuffer()->Size().Height();
       submitted_frame =
           Host()->PushFrame(Host()->ResourceProvider()->ProduceCanvasResource(),
                             SkIRect::MakeWH(width, height));