Add -XX:+DisableExplicitGC option for Art

Phone boots.  Also removed elfwriter spam from logcat.

Change-Id: I09b9d2fc40ebfeb6f1c2f12153b0ad4134bb5159
diff --git a/runtime/runtime.h b/runtime/runtime.h
index b93ae9d..8aba762 100644
--- a/runtime/runtime.h
+++ b/runtime/runtime.h
@@ -99,6 +99,7 @@
     bool is_zygote_;
     bool interpreter_only_;
     bool is_concurrent_gc_enabled_;
+    bool is_explicit_gc_disabled_;
     size_t heap_initial_size_;
     size_t heap_maximum_size_;
     size_t heap_growth_limit_;
@@ -146,6 +147,10 @@
     return is_concurrent_gc_enabled_;
   }
 
+  bool IsExplicitGcDisabled() const {
+    return is_explicit_gc_disabled_;
+  }
+
 #ifdef ART_SEA_IR_MODE
   bool IsSeaIRMode() const {
     return sea_ir_mode_;
@@ -405,6 +410,7 @@
   bool is_compiler_;
   bool is_zygote_;
   bool is_concurrent_gc_enabled_;
+  bool is_explicit_gc_disabled_;
 
   CompilerFilter compiler_filter_;
   size_t huge_method_threshold_;