Make the SwapChain interface match webgpu.h

This changes the methods of Dawn's SwapChain to match webgpu.h, namely
Present() now doesn't take arguments, and GetNextTexture() is replaced
with GetCurrentTextureView().

BUG=dawn:269

Change-Id: Ia0debefb170caf799c3310b1dad5535c4c5f59ca
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/13441
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
diff --git a/examples/CppHelloTriangle.cpp b/examples/CppHelloTriangle.cpp
index 0568278..05e7a5c 100644
--- a/examples/CppHelloTriangle.cpp
+++ b/examples/CppHelloTriangle.cpp
@@ -153,8 +153,8 @@
     s.b += 0.02f;
     if (s.b >= 1.0f) {s.b = 0.0f;}
 
-    wgpu::Texture backbuffer = swapchain.GetNextTexture();
-    utils::ComboRenderPassDescriptor renderPass({backbuffer.CreateView()}, depthStencilView);
+    wgpu::TextureView backbufferView = swapchain.GetCurrentTextureView();
+    utils::ComboRenderPassDescriptor renderPass({backbufferView}, depthStencilView);
 
     wgpu::CommandEncoder encoder = device.CreateCommandEncoder();
     {
@@ -169,7 +169,7 @@
 
     wgpu::CommandBuffer commands = encoder.Finish();
     queue.Submit(1, &commands);
-    swapchain.Present(backbuffer);
+    swapchain.Present();
     DoFlush();
 }