Revert "[wasm] Remove fixed limit on number of background tasks"

This reverts commit 54379af9.

Reason for revert: Big performance regressions, need to investigate

Original change's description:
> [wasm] Remove fixed limit on number of background tasks
> 
> After fixing https://crbug.com/v8/8916, background compilation scales
> far beyond 10 threads, especially for TurboFan (where much more work is
> parallelizable). Thus, remove the limit of 10 background compilation
> tasks, and use all available threads instead.
> 
> R=​mstarzinger@chromium.org
> 
> Bug: v8:8916
> Change-Id: I13c30777e3c85b2de7901b5eac3e6a41457a56f9
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1893348
> Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
> Commit-Queue: Clemens Backes <clemensb@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#64724}

TBR=mstarzinger@chromium.org,clemensb@chromium.org

Change-Id: I180cff9f39d8960aa793f279cfb61b7444992bc6
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:8916
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1897889Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64748}

src/flags/flag-definitions.h

@@ -641,9 +641,8 @@ DEFINE_BOOL(assume_asmjs_origin, false,
             "force wasm decoder to assume input is internal asm-wasm format")
 DEFINE_BOOL(wasm_disable_structured_cloning, false,
             "disable wasm structured cloning")
-DEFINE_INT(wasm_num_compilation_tasks, -1,
-           "number of parallel compilation tasks for wasm (default of -1 means "
-           "using all available threads)")
+DEFINE_INT(wasm_num_compilation_tasks, 10,
+           "number of parallel compilation tasks for wasm")
 DEFINE_DEBUG_BOOL(trace_wasm_native_heap, false,
                   "trace wasm native heap events")
 DEFINE_BOOL(wasm_write_protect_code_memory, false,

src/wasm/module-compiler.cc

@@ -2200,11 +2200,7 @@ bool AsyncStreamingProcessor::Deserialize(Vector<const uint8_t> module_bytes,
 int GetMaxBackgroundTasks() {
   if (NeedsDeterministicCompile()) return 0;
   int num_worker_threads = V8::GetCurrentPlatform()->NumberOfWorkerThreads();
-  int flag_limit = FLAG_wasm_num_compilation_tasks;
-  if (flag_limit >= 0) {
-    num_worker_threads = std::min(num_worker_threads, flag_limit);
-  }
-  return num_worker_threads;
+  return std::min(FLAG_wasm_num_compilation_tasks, num_worker_threads);
 }
 
 CompilationStateImpl::CompilationStateImpl(