Add -XX:+DisableExplicitGC option for Art

Phone boots.  Also removed elfwriter spam from logcat.

Change-Id: I09b9d2fc40ebfeb6f1c2f12153b0ad4134bb5159
diff --git a/runtime/native/java_lang_Runtime.cc b/runtime/native/java_lang_Runtime.cc
index e380c17..55575cf 100644
--- a/runtime/native/java_lang_Runtime.cc
+++ b/runtime/native/java_lang_Runtime.cc
@@ -28,6 +28,10 @@
 namespace art {
 
 static void Runtime_gc(JNIEnv*, jclass) {
+  if (Runtime::Current()->IsExplicitGcDisabled()) {
+      LOG(INFO) << "Explicit GC skipped.";
+      return;
+  }
   Runtime::Current()->GetHeap()->CollectGarbage(false);
 }