Make TypedArray.from and TypedArray.of writable and configurable

BUG=v8:4315
R=adamk
LOG=Y

Review URL: https://codereview.chromium.org/1734223004

Cr-Commit-Position: refs/heads/master@{#34310}

src/js/typedarray.js

@@ -785,7 +785,7 @@ function TypedArray() {
 %FunctionSetPrototype(TypedArray, new GlobalObject());
 %AddNamedProperty(TypedArray.prototype,
                   "constructor", TypedArray, DONT_ENUM);
-utils.InstallFunctions(TypedArray, DONT_ENUM | DONT_DELETE | READ_ONLY, [
+utils.InstallFunctions(TypedArray, DONT_ENUM, [
   "from", TypedArrayFrom,
   "of", TypedArrayOf
 ]);

test/mjsunit/es6/typedarray-of.js

@@ -115,9 +115,9 @@ function TestTypedArrayOf(constructor) {
   // Check superficial features of %TypedArray%.of.
   var desc = Object.getOwnPropertyDescriptor(constructor.__proto__, "of");
 
-  assertEquals(desc.configurable, false);
+  assertEquals(desc.configurable, true);
   assertEquals(desc.enumerable, false);
-  assertEquals(desc.writable, false);
+  assertEquals(desc.writable, true);
   assertEquals(constructor.of.length, 0);
 
   // %TypedArray%.of is not a constructor.