src: remove usages of GetBackingStore in crypto

src/crypto/README.md

@@ -112,12 +112,15 @@ the `ByteSource::Builder` without releasing it as a `ByteSource`.
 
 ### `ArrayBufferOrViewContents`
 
-The `ArrayBufferOfViewContents` class is a helper utility that abstracts
+The `ArrayBufferOrViewContents` class is a helper utility that abstracts
 `ArrayBuffer`, `TypedArray`, or `DataView` inputs and provides access to
 their underlying data pointers. It is used extensively through `src/crypto`
 to make it easier to deal with inputs that allow any `ArrayBuffer`-backed
 object.
 
+The lifetime of `ArrayBufferOrViewContents` should not exceed the
+lifetime of its input.
+
 ### Key objects
 
 Most crypto operations involve the use of keys -- cryptographic inputs

src/crypto/crypto_util.h

@@ -703,17 +703,17 @@ class ArrayBufferOrViewContents {
       auto view = buf.As<v8::ArrayBufferView>();
       offset_ = view->ByteOffset();
       length_ = view->ByteLength();
-      store_ = view->Buffer()->GetBackingStore();
+      data_ = view->Buffer()->Data();
     } else if (buf->IsArrayBuffer()) {
       auto ab = buf.As<v8::ArrayBuffer>();
       offset_ = 0;
       length_ = ab->ByteLength();
-      store_ = ab->GetBackingStore();
+      data_ = ab->Data();
     } else {
       auto sab = buf.As<v8::SharedArrayBuffer>();
       offset_ = 0;
       length_ = sab->ByteLength();
-      store_ = sab->GetBackingStore();
+      data_ = sab->Data();
     }
   }
 
@@ -723,7 +723,7 @@ class ArrayBufferOrViewContents {
     // length is zero, so we have to return something.
     if (size() == 0)
       return &buf;
-    return reinterpret_cast<T*>(store_->Data()) + offset_;
+    return reinterpret_cast<T*>(data_) + offset_;
   }
 
   inline T* data() {
@@ -732,7 +732,7 @@ class ArrayBufferOrViewContents {
     // length is zero, so we have to return something.
     if (size() == 0)
       return &buf;
-    return reinterpret_cast<T*>(store_->Data()) + offset_;
+    return reinterpret_cast<T*>(data_) + offset_;
   }
 
   inline size_t size() const { return length_; }
@@ -772,7 +772,7 @@ class ArrayBufferOrViewContents {
   T buf = 0;
   size_t offset_ = 0;
   size_t length_ = 0;
-  std::shared_ptr<v8::BackingStore> store_;
+  void* data_ = 0;
 };
 
 v8::MaybeLocal<v8::Value> EncodeBignum(