Supress failing end2end tests with Metal validation layer

The 3 tests run failed with Metal validation layer, which block end2end tests run with validation layer in CQ. Suppress temporarily while we're fixing.

BUG=dawn:139

Change-Id: I0b6c99ac731b90cd10b8b1f7bb5d3f5e1976fb07
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/8241
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
diff --git a/src/tests/DawnTest.cpp b/src/tests/DawnTest.cpp
index c567d49..aa95396 100644
--- a/src/tests/DawnTest.cpp
+++ b/src/tests/DawnTest.cpp
@@ -190,6 +190,10 @@
     return mUseWire;
 }
 
+bool DawnTestEnvironment::IsBackendValidationEnabled() const {
+    return mEnableBackendValidation;
+}
+
 dawn_native::Instance* DawnTestEnvironment::GetInstance() const {
     return mInstance.get();
 }
@@ -296,6 +300,10 @@
     return gTestEnv->UsesWire();
 }
 
+bool DawnTest::IsBackendValidationEnabled() const {
+    return gTestEnv->IsBackendValidationEnabled();
+}
+
 void DawnTest::SetUp() {
     // Get an adapter for the backend to use, and create the device.
     dawn_native::Adapter backendAdapter;