Fix sample presentMode value set

Now that default values are undefined,
set the SurfaceConfiguration::presentMode explicitly.

Change-Id: Ie8c7d7ad04e3307a0257ece27492f00865e2897a
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/237715
Auto-Submit: Shrek Shao <shrekshao@google.com>
Reviewed-by: Loko Kung <lokokung@google.com>
Commit-Queue: Shrek Shao <shrekshao@google.com>
Commit-Queue: Loko Kung <lokokung@google.com>
diff --git a/src/dawn/samples/SampleUtils.cpp b/src/dawn/samples/SampleUtils.cpp
index 7604916..e8040a5 100644
--- a/src/dawn/samples/SampleUtils.cpp
+++ b/src/dawn/samples/SampleUtils.cpp
@@ -326,6 +326,8 @@
     config.format = capabilities.formats[0];
     config.width = width;
     config.height = height;
+    DAWN_ASSERT(capabilities.presentModeCount > 0);
+    config.presentMode = capabilities.presentModes[0];
     surface.Configure(&config);
     this->preferredSurfaceTextureFormat = capabilities.formats[0];