Improve the generational mode.

- Turn the compile-time flags for generational mode into a command
  line flag.

- In the generational mode, always collect the whole heap, as opposed
  to the bump pointer space only, if a collection is an explicit,
  native allocation-triggered or last attempt one.

Change-Id: I7a14a707cc47e6e3aa4a3292db62533409f17563
diff --git a/runtime/gc/gc_cause.cc b/runtime/gc/gc_cause.cc
new file mode 100644
index 0000000..b25f7ff
--- /dev/null
+++ b/runtime/gc/gc_cause.cc
@@ -0,0 +1,45 @@
+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "gc_cause.h"
+#include "globals.h"
+#include "base/logging.h"
+
+#include <ostream>
+
+namespace art {
+namespace gc {
+
+const char* PrettyCause(GcCause cause) {
+  switch (cause) {
+    case kGcCauseForAlloc: return "Alloc";
+    case kGcCauseBackground: return "Background";
+    case kGcCauseExplicit: return "Explicit";
+    case kGcCauseForNativeAlloc: return "NativeAlloc";
+    case kGcCauseCollectorTransition: return" CollectorTransition";
+    default:
+      LOG(FATAL) << "Unreachable";
+  }
+  return "";
+}
+
+std::ostream& operator<<(std::ostream& os, const GcCause& gc_cause) {
+  os << PrettyCause(gc_cause);
+  return os;
+}
+
+}  // namespace gc
+}  // namespace art