Remove default heap size limit and add separate limit for externals.

runtime/vm/heap.cc

Index: runtime/vm/heap.cc
===================================================================
--- runtime/vm/heap.cc	(revision 43108)
+++ runtime/vm/heap.cc	(working copy)
@@ -43,7 +43,8 @@
 
 Heap::Heap(Isolate* isolate,
            intptr_t max_new_gen_semi_words,
-           intptr_t max_old_gen_words)
+           intptr_t max_old_gen_words,
+           intptr_t max_external_words)
     : isolate_(isolate),
       read_only_(false),
       gc_in_progress_(false),
@@ -57,7 +58,7 @@
   new_space_ = new Scavenger(this,
                              max_new_gen_semi_words,
                              kNewObjectAlignmentOffset);
-  old_space_ = new PageSpace(this, max_old_gen_words);
+  old_space_ = new PageSpace(this, max_old_gen_words, max_external_words);
   stats_.num_ = 0;
 }
 
@@ -434,9 +435,13 @@
 
 void Heap::Init(Isolate* isolate,
                 intptr_t max_new_gen_words,
-                intptr_t max_old_gen_words) {
+                intptr_t max_old_gen_words,
+                intptr_t max_external_words) {
   ASSERT(isolate->heap() == NULL);
-  Heap* heap = new Heap(isolate, max_new_gen_words, max_old_gen_words);
+  Heap* heap = new Heap(isolate,
+                        max_new_gen_words,
+                        max_old_gen_words,
+                        max_external_words);
   isolate->set_heap(heap);
 }