Simpler API for allocation tracking

[samreid]

The current rules for allocation tracking are:

/**
 * 1. Run the sim and set up the scenario that you wish to profile
 * 2. In the JS console, type: window.alloc={}
 * 3. Wait until you have taken enough data
 * 4. Type x = window.alloc; delete window.alloc;
 *
 * Now you can inspect the x variable which contains the allocation information.
 */

I think it would be simpler if we made the made the api more like:

/**
 * 1. Run the sim and set up the scenario that you wish to profile
 * 2. In the JS console, type: window.recordAllocations = true;
 * 3. Wait until you have taken enough data
 * 4. Type window.recordAllocations = false;
 *
 * Now you can inspect window.allocations.
 */

If we cannot add ES5 get/set onto window, then functions could be used instead.

We should also provide reports by frequency (not by count) so that different runs can easily be compared.