[api] Create SharedMemoryStatistics API

Creates new APIs to get Shared Memory statistics like the size of
read-only space and potentially the memory used by shared array buffers.

Currently all shared memory statistics are zero.

Bug: v8:7464
Change-Id: Ib8d58f885beaa1d65ccef7b64dd4f3db4149bca3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1900465
Commit-Queue: Dan Elphick <delphick@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64831}

include/v8.h

@@ -7453,10 +7453,31 @@ typedef void (*InterruptCallback)(Isolate* isolate, void* data);
 typedef size_t (*NearHeapLimitCallback)(void* data, size_t current_heap_limit,
                                         size_t initial_heap_limit);
 
+/**
+ * Collection of shared per-process V8 memory information.
+ *
+ * Instances of this class can be passed to
+ * v8::Isolate::GetSharedMemoryStatistics to get shared memory statistics from
+ * V8.
+ */
+class V8_EXPORT SharedMemoryStatistics {
+ public:
+  SharedMemoryStatistics();
+  size_t total_read_only_space_size() { return total_read_only_space_size_; }
+  size_t total_size() { return total_size_; }
+
+ private:
+  size_t total_read_only_space_size_;
+  size_t total_size_;
+
+  friend class V8;
+  friend class Isolate;
+};
+
 /**
  * Collection of V8 heap information.
  *
- * Instances of this class can be passed to v8::V8::HeapStatistics to
+ * Instances of this class can be passed to v8::Isolate::GetHeapStatistics to
  * get heap statistics from V8.
  */
 class V8_EXPORT HeapStatistics {
@@ -8420,6 +8441,11 @@ class V8_EXPORT Isolate {
   template <class T>
   V8_INLINE MaybeLocal<T> GetDataFromSnapshotOnce(size_t index);
 
+  /**
+   * Get statistics about the shared memory usage.
+   */
+  void GetSharedMemoryStatistics(SharedMemoryStatistics* statistics);
+
   /**
    * Get statistics about the heap memory usage.
    */

src/api/api.cc

@@ -5708,6 +5708,9 @@ bool v8::V8::Dispose() {
   return true;
 }
 
+SharedMemoryStatistics::SharedMemoryStatistics()
+    : total_read_only_space_size_(0), total_size_(0) {}
+
 HeapStatistics::HeapStatistics()
     : total_heap_size_(0),
       total_heap_size_executable_(0),
@@ -8470,6 +8473,11 @@ i::Address* Isolate::GetDataFromSnapshotOnce(size_t index) {
   return GetSerializedDataFromFixedArray(i_isolate, list, index);
 }
 
+void Isolate::GetSharedMemoryStatistics(SharedMemoryStatistics* statistics) {
+  statistics->total_read_only_space_size_ = 0;
+  statistics->total_size_ = 0;
+}
+
 void Isolate::GetHeapStatistics(HeapStatistics* heap_statistics) {
   i::Isolate* isolate = reinterpret_cast<i::Isolate*>(this);
   i::Heap* heap = isolate->heap();