End2EndTests: Fix -w runs without ASSERTs enabled.

The flushing of command buffers was in an ASSERT which made them skipped
on release builds.

BUG=

Change-Id: I07bf558d1689f4bea0047a80ab3c8b04938f04a0
Reviewed-on: https://dawn-review.googlesource.com/c/4501
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
diff --git a/src/tests/DawnTest.cpp b/src/tests/DawnTest.cpp
index c643047..357c090 100644
--- a/src/tests/DawnTest.cpp
+++ b/src/tests/DawnTest.cpp
@@ -332,8 +332,10 @@
 
 void DawnTest::FlushWire() {
     if (gTestUsesWire) {
-        ASSERT(mC2sBuf->Flush());
-        ASSERT(mS2cBuf->Flush());
+        bool C2SFlushed = mC2sBuf->Flush();
+        bool S2CFlushed = mS2cBuf->Flush();
+        ASSERT(C2SFlushed);
+        ASSERT(S2CFlushed);
     }
 }