ART: Swap-space in the compiler

Introduce a swap-space and corresponding allocator to transparently
switch native allocations to memory backed by a file.

Bug: 18596910

(cherry picked from commit 62746d8d9c4400e4764f162b22bfb1a32be287a9)

Change-Id: I131448f3907115054a592af73db86d2b9257ea33
diff --git a/compiler/utils/assembler.h b/compiler/utils/assembler.h
index 67711e3..134dda4 100644
--- a/compiler/utils/assembler.h
+++ b/compiler/utils/assembler.h
@@ -502,6 +502,8 @@
 
   virtual void InitializeFrameDescriptionEntry() {}
   virtual void FinalizeFrameDescriptionEntry() {}
+  // Give a vector containing FDE data, or null if not used. Note: the assembler must take care
+  // of handling the lifecycle.
   virtual std::vector<uint8_t>* GetFrameDescriptionEntry() { return nullptr; }
 
   virtual ~Assembler() {}