Reland "Fix WebGL PushFrame crash when GetDrawingBuffer returns NULL"

This reverts commit 34ad7c1a.

Reason for revert: <This is not one which breaks the GPU FYI bots>

Original change's description:
> 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/+/2109460
> Reviewed-by: Maggie Chen <magchen@chromium.org>
> Commit-Queue: Maggie Chen <magchen@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#751623}

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

Change-Id: I2a74f8f550378381ae4a0af7f54fe42979147768
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1059491
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2106998Reviewed-by: Maggie Chen <magchen@chromium.org>
Commit-Queue: Maggie Chen <magchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#751634}

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));