[wasm] Switch {outstanding_finishers} to {std::atomic}.

R=clemensh@chromium.org
BUG=v8:7754

Change-Id: Ic6157ab1219bcdbdb6ac751d05602ab411d58ce2
Reviewed-on: https://chromium-review.googlesource.com/1117072
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54065}

src/wasm/module-compiler.cc

@@ -2547,7 +2547,7 @@ class AsyncCompileJob::PrepareAndStartCompile : public CompileStep {
                 // foreground task is currently pending, and no finisher is
                 // outstanding (streaming compilation).
                 if (job->num_pending_foreground_tasks_ == 0 &&
-                    job->outstanding_finishers_.Value() == 0) {
+                    job->outstanding_finishers_.load() == 0) {
                   job->isolate_->wasm_engine()->RemoveCompileJob(job);
                 } else {
                   // If a foreground task was pending or a finsher was pending,
@@ -2766,7 +2766,7 @@ bool AsyncStreamingProcessor::ProcessCodeSectionHeader(size_t functions_count,
 
   // Set outstanding_finishers_ to 2, because both the AsyncCompileJob and the
   // AsyncStreamingProcessor have to finish.
-  job_->outstanding_finishers_.SetValue(2);
+  job_->outstanding_finishers_.store(2);
   compilation_unit_builder_.reset(
       new CompilationUnitBuilder(job_->native_module_));
   return true;

src/wasm/module-compiler.h

@@ -5,10 +5,10 @@
 #ifndef V8_WASM_MODULE_COMPILER_H_
 #define V8_WASM_MODULE_COMPILER_H_
 
+#include <atomic>
 #include <functional>
 #include <memory>
 
-#include "src/base/atomic-utils.h"
 #include "src/cancelable-task.h"
 #include "src/globals.h"
 #include "src/wasm/wasm-module.h"
@@ -162,13 +162,13 @@ class AsyncCompileJob {
   // For async compilation the AsyncCompileJob is the only finisher. For
   // streaming compilation also the AsyncStreamingProcessor has to finish before
   // compilation can be finished.
-  base::AtomicNumber<int32_t> outstanding_finishers_{1};
+  std::atomic<int32_t> outstanding_finishers_{1};
 
   // Decrements the number of outstanding finishers. The last caller of this
   // function should finish the asynchronous compilation, see the comment on
   // {outstanding_finishers_}.
   V8_WARN_UNUSED_RESULT bool DecrementAndCheckFinisherCount() {
-    return outstanding_finishers_.Decrement(1) == 0;
+    return outstanding_finishers_.fetch_sub(1) == 1;
   }
 
   // Counts the number of pending foreground tasks.