Corrected resubmssion of r34736.

runtime/vm/pages.h

Index: runtime/vm/pages.h
===================================================================
--- runtime/vm/pages.h	(revision 34741)
+++ runtime/vm/pages.h	(working copy)
@@ -7,6 +7,7 @@
 
 #include "vm/freelist.h"
 #include "vm/globals.h"
+#include "vm/spaces.h"
 #include "vm/virtual_memory.h"
 
 namespace dart {
@@ -116,14 +117,18 @@
                       int garbage_collection_time_ratio);
   ~PageSpaceController();
 
-  bool CanGrowPageSpace(intptr_t size_in_bytes);
+  // Returns whether growing to 'after' should trigger a GC.
+  // This method can be called before allocation (e.g., pretenuring) or after
+  // (e.g., promotion), as it does not change the state of the controller.
+  bool NeedsGarbageCollection(SpaceUsage after) const;
 
+  // Should be called after each collection to update the controller state.
   // A garbage collection is considered as successful if more than
   // heap_growth_ratio % of memory got deallocated by the garbage collector.
   // In this case garbage collection will be performed next time. Otherwise
   // the heap will grow.
-  void EvaluateGarbageCollection(intptr_t used_before_in_words,
-                                 intptr_t used_after_in_words,
+  void EvaluateGarbageCollection(SpaceUsage before,
+                                 SpaceUsage after,
                                  int64_t start, int64_t end);
 
   int64_t last_code_collection_in_us() { return last_code_collection_in_us_; }
@@ -141,6 +146,9 @@
  private:
   bool is_enabled_;
 
+  // Usage after last evaluated GC.
+  SpaceUsage last_usage_;
+
   // Heap growth control variable.
   intptr_t grow_heap_;
 
@@ -186,11 +194,16 @@
                     HeapPage::PageType type = HeapPage::kData,
                     GrowthPolicy growth_policy = kControlGrowth);
 
-  intptr_t UsedInWords() const { return used_in_words_; }
-  intptr_t CapacityInWords() const { return capacity_in_words_; }
+  bool NeedsGarbageCollection() const {
+    return page_space_controller_.NeedsGarbageCollection(usage_);
+  }
+
+  intptr_t UsedInWords() const { return usage_.used_in_words; }
+  intptr_t CapacityInWords() const { return usage_.capacity_in_words; }
   intptr_t ExternalInWords() const {
-    return external_in_words_;
+    return usage_.external_in_words;
   }
+  SpaceUsage GetCurrentUsage() const { return usage_; }
 
   bool Contains(uword addr) const;
   bool Contains(uword addr, HeapPage::PageType type) const;
@@ -222,7 +235,7 @@
   }
 
   bool NeedExternalGC() {
-    return used_in_words_ + ExternalInWords() > max_capacity_in_words_;
+    return UsedInWords() + ExternalInWords() > max_capacity_in_words_;
   }
 
   void WriteProtect(bool read_only);
@@ -275,8 +288,8 @@
   static intptr_t LargePageSizeInWordsFor(intptr_t size);
 
   bool CanIncreaseCapacityInWords(intptr_t increase_in_words) {
-    ASSERT(capacity_in_words_ <= max_capacity_in_words_);
-    return increase_in_words <= (max_capacity_in_words_ - capacity_in_words_);
+    ASSERT(CapacityInWords() <= max_capacity_in_words_);
+    return increase_in_words <= (max_capacity_in_words_ - CapacityInWords());
   }
 
   FreeList freelist_[HeapPage::kNumPageTypes];
@@ -289,9 +302,7 @@
 
   // Various sizes being tracked for this generation.
   intptr_t max_capacity_in_words_;
-  intptr_t capacity_in_words_;
-  intptr_t used_in_words_;
-  intptr_t external_in_words_;
+  SpaceUsage usage_;
 
   // Keep track whether a MarkSweep is currently running.
   bool sweeping_;