[wasm] Avoid double accounting for wasm memory reservations

Currently the total allocated address space is collected twice per Wasm
memory: Once on allocation, once on release. Recording it once provides
the same data.

R=titzer@chromium.org

Bug: v8:8975
Change-Id: I99719ecb44b14ce5da1be4a74291377f91f4038a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1514738Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60164}

src/wasm/wasm-memory.cc

@@ -214,7 +214,10 @@ void WasmMemoryTracker::RegisterAllocation(Isolate* isolate,
   base::MutexGuard scope_lock(&mutex_);
 
   allocated_address_space_ += allocation_length;
-  AddAddressSpaceSample(isolate);
+  // Report address space usage in MiB so the full range fits in an int on all
+  // platforms.
+  isolate->counters()->wasm_address_space_usage_mb()->AddSample(
+      static_cast<int>(allocated_address_space_ / MB));
 
   allocations_.emplace(buffer_start,
                        AllocationData{allocation_base, allocation_length,
@@ -231,10 +234,6 @@ WasmMemoryTracker::AllocationData WasmMemoryTracker::ReleaseAllocation_Locked(
   DCHECK_LE(num_bytes, allocated_address_space_);
   reserved_address_space_ -= num_bytes;
   allocated_address_space_ -= num_bytes;
-  // ReleaseAllocation might be called with a nullptr as isolate if the
-  // embedder is releasing the allocation and not a specific isolate. This
-  // happens if the allocation was shared between multiple isolates (threads).
-  if (isolate) AddAddressSpaceSample(isolate);
 
   AllocationData allocation_data = find_result->second;
   allocations_.erase(find_result);
@@ -565,13 +564,6 @@ void WasmMemoryTracker::DeleteSharedMemoryObjectsOnIsolate(Isolate* isolate) {
   }
 }
 
-void WasmMemoryTracker::AddAddressSpaceSample(Isolate* isolate) {
-  // Report address space usage in MiB so the full range fits in an int on all
-  // platforms.
-  isolate->counters()->wasm_address_space_usage_mb()->AddSample(
-      static_cast<int>(allocated_address_space_ >> 20));
-}
-
 Handle<JSArrayBuffer> SetupArrayBuffer(Isolate* isolate, void* backing_store,
                                        size_t size, bool is_external,
                                        SharedFlag shared) {

src/wasm/wasm-memory.h

@@ -214,7 +214,6 @@ class WasmMemoryTracker {
   AllocationData ReleaseAllocation_Locked(Isolate* isolate,
                                           const void* buffer_start);
 
-  void AddAddressSpaceSample(Isolate* isolate);
   // Clients use a two-part process. First they "reserve" the address space,
   // which signifies an intent to actually allocate it. This determines whether
   // doing the allocation would put us over our limit. Once there is a