[node] Add Buffer.poolSize() and correct Buffer.byteLength() (#20419)

* [node] Add Buffer.poolSize

* [node] Allow more types for Buffer.byteLength()

* fix lint issue

types/node/index.d.ts

@@ -239,10 +239,10 @@ declare var Buffer: {
      * Gives the actual byte length of a string. encoding defaults to 'utf8'.
      * This is not the same as String.prototype.length since that returns the number of characters in a string.
      *
-     * @param string string to test.
+     * @param string string to test. (TypedArray is also allowed, but it is only available starting ES2017)
      * @param encoding encoding used to evaluate (defaults to 'utf8')
      */
-    byteLength(string: string, encoding?: string): number;
+    byteLength(string: string | Buffer | DataView | ArrayBuffer, encoding?: string): number;
     /**
      * Returns a buffer which is the result of concatenating all the buffers in the list together.
      *
@@ -282,6 +282,10 @@ declare var Buffer: {
      * @param size count of octets to allocate
      */
     allocUnsafeSlow(size: number): Buffer;
+    /**
+     * This is the number of bytes used to determine the size of pre-allocated, internal Buffer instances used for pooling. This value may be modified.
+     */
+    poolSize: number;
 };
 
 /************************************************

types/node/node-tests.ts

@@ -396,6 +396,32 @@ function bufferTests() {
         const buf2: Buffer = Buffer.from('7468697320697320612074c3a97374', 'hex');
     }
 
+    // Class Method byteLenght
+    {
+        let len: number;
+        len = Buffer.byteLength("foo");
+        len = Buffer.byteLength("foo", "utf8");
+
+        const b = Buffer.from("bar");
+        len = Buffer.byteLength(b);
+        len = Buffer.byteLength(b, "utf16le");
+
+        const ab = new ArrayBuffer(15);
+        len = Buffer.byteLength(ab);
+        len = Buffer.byteLength(ab, "ascii");
+
+        const dv = new DataView(ab);
+        len = Buffer.byteLength(dv);
+        len = Buffer.byteLength(dv, "utf16le");
+    }
+
+    // Class Method poolSize
+    {
+        let s: number;
+        s = Buffer.poolSize;
+        Buffer.poolSize = 4096;
+    }
+
     // Test that TS 1.6 works with the 'as Buffer' annotation
     // on isBuffer.
     var a: Buffer | number;