DebugBreak in ThreadContext::AssertJsReentrancy

````
var A = new Uint32Array(10000);

function foo()
{
for (var i = 0; i < 10000; i++) {
A[i] = 0x1234;
}

for (var i = 0; i < 10000; i++)
{
A[i] = foo;
}
}

var r;

for (var i = 0; i < 1000; i++)
{
print(i);
r = foo();
}
````