Include a new heap summary line in the SIGQUIT output.

Looks like this:

  Heap: 87% free, 4MB/32MB; 6327 objects

While I'm here, fix another long-standing TODO to make PrettySize have the
usual google3 behavior. (I took the specific thresholds from Chromium.)

Also distinguish between the more general "Dump" member functions and the
specific SIGQUIT-related ones by consistently calling the latter DumpForSigQuit.

Change-Id: I76e783adc18dd089bac9b348f53dc9860a0fe4b9
diff --git a/src/heap.h b/src/heap.h
index 7717871..3f0ffc0 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -17,6 +17,7 @@
 #ifndef ART_SRC_HEAP_H_
 #define ART_SRC_HEAP_H_
 
+#include <iosfwd>
 #include <string>
 #include <vector>
 
@@ -219,6 +220,8 @@
     return alloc_space_;
   }
 
+  void DumpForSigQuit(std::ostream& os);
+
  private:
   // Allocates uninitialized storage.
   Object* AllocateLocked(size_t num_bytes);
@@ -239,6 +242,8 @@
   // collection.
   void GrowForUtilization();
 
+  size_t GetPercentFree();
+
   void AddSpace(Space* space);
 
   void VerifyObjectLocked(const Object *obj);