Make adding crash keys thread safe

Bug: chromium:977893
Change-Id: Ibd4be9b9ce13bcb8aca4b6ac6d7a1c56a01e39d9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1676606Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Irina Yatsenko <irinayat@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#62392}

src/diagnostics/crash-key.cc

@@ -33,7 +33,9 @@ static CrashKeyInstance crash_keys[] = {
 };
 
 void AddCrashKey(int id, const char* name, uintptr_t value) {
-  static int current = 0;
+  static std::atomic<int> last{-1};
+  const int current = ++last;
+
   if (current > kMaxCrashKeysCount) {
     return;
   }
@@ -41,7 +43,6 @@ void AddCrashKey(int id, const char* name, uintptr_t value) {
   if (current == kMaxCrashKeysCount) {
     static crash_reporter::CrashKeyString<1> over("v8-too-many-keys");
     over.Set("1");
-    current++;
     return;
   }
 
@@ -50,8 +51,6 @@ void AddCrashKey(int id, const char* name, uintptr_t value) {
   std::stringstream stream;
   stream << name << " " << id << " 0x" << std::hex << value;
   trace_key.Set(stream.str().substr(0, kKeySize));
-
-  current++;
 }
 
 }  // namespace crash