Revert "Enable -Wunreachable-code in Fuchsia builds."

This reverts commit ec7d2855.

Reason for revert: Breaks the Fuchsia Cast bots due to unreachable code under //chromecast. We'll need to fix //chromecast to re-land.

Original change's description:
> Enable -Wunreachable-code in Fuchsia builds.
> 
> Depends on https://chromium-review.googlesource.com/c/angle/angle/+/2112281
> 
> Bug: 346399
> Change-Id: I6bf27dc15303c207be0ae85dd3256af217db005b
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2111833
> Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
> Commit-Queue: Nico Weber <thakis@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#752299}

TBR=wez@chromium.org,thakis@chromium.org,kmarshall@chromium.org,sergeyu@chromium.org

Change-Id: Id094305ad1df897b8a12bb93d76b5feca5d96f27
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 346399, 1063669
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2114271Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#752334}

build/config/compiler/BUILD.gn

@@ -1591,8 +1591,7 @@ config("chromium_code") {
 
     # TODO(thakis): Enable this more often, https://crbug.com/346399
     # use_libfuzzer: https://crbug.com/1063180
-    if (!is_nacl && !use_libfuzzer &&
-        (target_os == "fuchsia" || target_os == "linux")) {
+    if (!is_nacl && target_os == "linux" && !use_libfuzzer) {
       cflags += [ "-Wunreachable-code" ]
     }
 

fuchsia/runners/common/web_content_runner.cc

@@ -74,9 +74,8 @@ void WebContentRunner::StartComponent(
       this,
       std::make_unique<base::fuchsia::StartupContext>(std::move(startup_info)),
       std::move(controller_request));
-#if BUILDFLAG(WEB_RUNNER_REMOTE_DEBUGGING_PORT) != 0
-  component->EnableRemoteDebugging();
-#endif
+  if (BUILDFLAG(WEB_RUNNER_REMOTE_DEBUGGING_PORT) != 0)
+    component->EnableRemoteDebugging();
   component->StartComponent();
   component->LoadUrl(url, std::vector<fuchsia::net::http::Header>());
   RegisterComponent(std::move(component));

fuchsia/runners/web/main.cc

@@ -42,10 +42,10 @@ int main(int argc, char** argv) {
       base::FilePath(base::fuchsia::kPersistedDataDirectoryPath)));
   CHECK(create_context_params.data_directory());
 
-#if BUILDFLAG(WEB_RUNNER_REMOTE_DEBUGGING_PORT) != 0
-  create_context_params.set_remote_debugging_port(
-      BUILDFLAG(WEB_RUNNER_REMOTE_DEBUGGING_PORT));
-#endif
+  if (BUILDFLAG(WEB_RUNNER_REMOTE_DEBUGGING_PORT) != 0) {
+    create_context_params.set_remote_debugging_port(
+        BUILDFLAG(WEB_RUNNER_REMOTE_DEBUGGING_PORT));
+  }
 
   WebContentRunner runner(
       std::move(create_context_params),

third_party/blink/renderer/platform/scheduler/common/thread_cpu_throttler.cc

@@ -167,16 +167,15 @@ void ThreadCPUThrottler::ThrottlingThread::Throttle() {
 }
 
 void ThreadCPUThrottler::ThrottlingThread::Start() {
-#if defined(USE_SIGNALS) || defined(OS_WIN)
-#if defined(USE_SIGNALS)
+#ifdef USE_SIGNALS
   InstallSignalHandler();
+#elif !defined(OS_WIN)
+  LOG(ERROR) << "CPU throttling is not supported.";
+  return;
 #endif
   if (!base::PlatformThread::Create(0, this, &throttling_thread_handle_)) {
     LOG(ERROR) << "Failed to create throttling thread.";
   }
-#else
-  LOG(ERROR) << "CPU throttling is not supported.";
-#endif
 }
 
 void ThreadCPUThrottler::ThrottlingThread::Sleep(base::TimeDelta duration) {