Change extern const DawnTestParam helpers to functions

If these extern variables are initialized after DAWN_INSTANTIATE_TEST,
they will be zero. Change them to be function calls instead.
Since they're function calls, fold in arguments from ForceToggles to
enable/disable toggles.

Bug: dawn:341
Change-Id: I1aeaa1e535a0a003977e8ce7ab3d5278c5d81281
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/16162
Reviewed-by: Mark Henderson <mehe@google.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>
diff --git a/src/tests/end2end/GpuMemorySynchronizationTests.cpp b/src/tests/end2end/GpuMemorySynchronizationTests.cpp
index 995d272..edc5994 100644
--- a/src/tests/end2end/GpuMemorySynchronizationTests.cpp
+++ b/src/tests/end2end/GpuMemorySynchronizationTests.cpp
@@ -231,7 +231,7 @@
     EXPECT_PIXEL_RGBA8_EQ(RGBA8(2, 0, 0, 255), renderPass.color, 0, 0);
 }
 
-DAWN_INSTANTIATE_TEST(GpuMemorySyncTests, D3D12Backend, MetalBackend, OpenGLBackend, VulkanBackend);
+DAWN_INSTANTIATE_TEST(GpuMemorySyncTests, D3D12Backend(), MetalBackend(), OpenGLBackend(), VulkanBackend());
 
 class StorageToUniformSyncTests : public DawnTest {
   protected:
@@ -415,10 +415,10 @@
 }
 
 DAWN_INSTANTIATE_TEST(StorageToUniformSyncTests,
-                      D3D12Backend,
-                      MetalBackend,
-                      OpenGLBackend,
-                      VulkanBackend);
+                      D3D12Backend(),
+                      MetalBackend(),
+                      OpenGLBackend(),
+                      VulkanBackend());
 
 constexpr int kRTSize = 8;
 constexpr int kVertexBufferStride = 4 * sizeof(float);
@@ -689,7 +689,7 @@
 }
 
 DAWN_INSTANTIATE_TEST(MultipleWriteThenMultipleReadTests,
-                      D3D12Backend,
-                      MetalBackend,
-                      OpenGLBackend,
-                      VulkanBackend);
+                      D3D12Backend(),
+                      MetalBackend(),
+                      OpenGLBackend(),
+                      VulkanBackend());