Compilation filter

This CL introduces a static compilation filter mechanism intended
to allow us to reduce compilation time and space requirements until
we have a profiling mechanism in place.

It supports 5 modes of filtering:

   o interpret-only (compile nothing)
   o deferred-compilation (compile only those methods believe to be
     compute-intensive)
   o space (optimized for space)
   o balanced (best return on space investment)
   o speed (compile everything)

A future CL will allow the default filtering mode to be set
via system property.  For now, you can pass it in via command
line as follows:

   dalvikvm -compiler-filter:[interpret-only|defer-compilation|
                              space|balanced|speed]

or dex2oat --runtime-arg -compiler-filter:[one of the above modes]

Creating a file named art/SMALL_ART will force the filter
default to interpret-only.  Later on we'll move this capability
to a persistent system property.

or modify kDefaultCompilerFilter in runtime.h

It also changes the compiler driver to allow the compilers to
decline to compile a method by return NULL.

Change-Id: Ic73411818f8bb845a4a19a05b0395c50902c534f
diff --git a/compiler/dex/frontend.h b/compiler/dex/frontend.h
index 5c68ab4..bafa468 100644
--- a/compiler/dex/frontend.h
+++ b/compiler/dex/frontend.h
@@ -77,6 +77,7 @@
   kDebugDumpBitcodeFile,
   kDebugVerifyBitcode,
   kDebugShowSummaryMemoryUsage,
+  kDebugShowFilterStats,
 };
 
 class LLVMInfo {