Reduce fuzzer log spam

When fuzzing, silence all LogMessages as errors frequently come up.
Suppressing logs should make the fuzzer more efficient.

Bug: none
Change-Id: I827625446c2afc3771ebf14d676b4e211d99dbda
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/91601
Reviewed-by: Loko Kung <lokokung@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Austin Eng <enga@chromium.org>

src/dawn/common/BUILD.gn

@@ -49,8 +49,13 @@ config("internal_config") {
   }
 
   if (use_fuzzing_engine) {
+    defines += [
       # Does a hard abort when an assertion fails so that fuzzers catch and parse the failure.
-    defines += [ "DAWN_ABORT_ON_ASSERT" ]
+      "DAWN_ABORT_ON_ASSERT",
+
+      # Disable logging to make fuzzing more efficient.
+      "DAWN_DISABLE_LOGGING",
+    ]
   }
 
   if (dawn_enable_d3d12) {

src/dawn/common/Log.cpp

@@ -71,6 +71,11 @@ LogMessage::LogMessage(LogMessage&& other) = default;
 LogMessage& LogMessage::operator=(LogMessage&& other) = default;
 
 LogMessage::~LogMessage() {
+#if defined(DAWN_DISABLE_LOGGING)
+    // Don't print logs to make fuzzing more efficient. Implemented as
+    // an early return to avoid warnings about unused member variables.
+    return;
+#endif
     std::string fullMessage = mStream.str();
 
     // If this message has been moved, its stream is empty.