[Fuchsia] Support --enable-logging=stderr and use in browser tests.

- Support --enable-logging and allow it to be used to enable logging
  to stderr.
- Add --enable-logging=stderr to the command-line in WebEngine
  browser-tests.

Bug: 968387
Change-Id: Ie29db5b086beac7867c0b01746006814a9759517
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1732673
Auto-Submit: Wez <wez@chromium.org>
Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683847}

fuchsia/engine/test/web_engine_test_launcher.cc

@@ -57,9 +57,10 @@ class WebEngineTestLauncherDelegate : public content::TestLauncherDelegate {
 
 int main(int argc, char** argv) {
   base::CommandLine::Init(argc, argv);
-  base::CommandLine::ForCurrentProcess()->AppendSwitchASCII(
-      switches::kOzonePlatform, "headless");
-  base::CommandLine::ForCurrentProcess()->AppendSwitch(switches::kDisableGpu);
+  auto* command_line = base::CommandLine::ForCurrentProcess();
+  command_line->AppendSwitchASCII(switches::kOzonePlatform, "headless");
+  command_line->AppendSwitchASCII(switches::kEnableLogging, "stderr");
+  command_line->AppendSwitch(switches::kDisableGpu);
 
   size_t parallel_jobs = base::NumParallelJobs();
   if (parallel_jobs > 1U) {

fuchsia/engine/web_engine_main_delegate.cc

@@ -24,7 +24,11 @@ WebEngineMainDelegate* g_current_web_engine_main_delegate = nullptr;
 
 void InitLoggingFromCommandLine(const base::CommandLine& command_line) {
   logging::LoggingSettings settings;
-  settings.logging_dest = logging::LOG_TO_SYSTEM_DEBUG_LOG;
+  if (command_line.GetSwitchValueASCII(switches::kEnableLogging) == "stderr") {
+    settings.logging_dest = logging::LOG_TO_STDERR;
+  } else {
+    settings.logging_dest = logging::LOG_TO_SYSTEM_DEBUG_LOG;
+  }
   if (command_line.HasSwitch(switches::kLogFile)) {
     settings.logging_dest |= logging::LOG_TO_FILE;
     settings.log_file =