Add command line options to specify the various heap size parameters.

vm/heap.h

Index: vm/heap.h
===================================================================
--- vm/heap.h	(revision 1042)
+++ vm/heap.h	(working copy)
@@ -29,6 +29,10 @@
     kExecutable
   };
 
+  // Default allocation sizes in MB for the old gen and code heaps.
+  static const intptr_t kHeapSizeInMB = 512;
+  static const intptr_t kCodeHeapSizeInMB = 4;
+
   ~Heap();
 
   uword Allocate(intptr_t size, Space space) {
@@ -69,10 +73,6 @@
   uword AllocateOld(intptr_t size);
   uword AllocateCode(intptr_t size);
 
-  // Allocation is limited to the below sizes.
-  static const intptr_t kHeapSize = 512 * MB;
-  static const intptr_t kCodeHeapSize = 4 * MB;
-
   // The different spaces used for allocation.
   Scavenger* new_space_;
   PageSpace* old_space_;