More advanced timing loggers.

The new timing loggers have lower overhead since they only push into
a vector. The new format has two types, a start timing and a stop
timing. You can thing of these as brackets associated with a
timestamp. It uses these to construct various statistics when needed,
such as: Total time, exclusive time, and nesting depth.

Changed PrettyDuration to have a default of 3 digits after the decimal
point.

Exaple of a GC dump with exclusive / total times and indenting:
I/art     (23546): GC iteration timing logger [Exclusive time] [Total time]
I/art     (23546):   0ms InitializePhase
I/art     (23546):   0.305ms/167.746ms MarkingPhase
I/art     (23546):     0ms BindBitmaps
I/art     (23546):     0ms FindDefaultSpaceBitmap
I/art     (23546):     0ms/1.709ms ProcessCards
I/art     (23546):       0.183ms ImageModUnionClearCards
I/art     (23546):       0.916ms ZygoteModUnionClearCards
I/art     (23546):       0.610ms AllocSpaceClearCards
I/art     (23546):       1.373ms AllocSpaceClearCards
I/art     (23546):     0.305ms/6.318ms MarkRoots
I/art     (23546):       2.106ms MarkRootsCheckpoint
I/art     (23546):       0.153ms MarkNonThreadRoots
I/art     (23546):       4.287ms MarkConcurrentRoots
I/art     (23546):     43.461ms UpdateAndMarkImageModUnionTable
I/art     (23546):     0ms/112.712ms RecursiveMark
I/art     (23546):       112.712ms ProcessMarkStack
I/art     (23546):     0.610ms/2.777ms PreCleanCards
I/art     (23546):       0.305ms/0.855ms ProcessCards
I/art     (23546):         0.153ms ImageModUnionClearCards
I/art     (23546):         0.610ms ZygoteModUnionClearCards
I/art     (23546):         0.610ms AllocSpaceClearCards
I/art     (23546):         0.549ms AllocSpaceClearCards
I/art     (23546):       0.549ms MarkRootsCheckpoint
I/art     (23546):       0.610ms MarkNonThreadRoots
I/art     (23546):       0ms MarkConcurrentRoots
I/art     (23546):       0.610ms ScanGrayImageSpaceObjects
I/art     (23546):       0.305ms ScanGrayZygoteSpaceObjects
I/art     (23546):       0.305ms ScanGrayAllocSpaceObjects
I/art     (23546):       1.129ms ScanGrayAllocSpaceObjects
I/art     (23546):       0ms ProcessMarkStack
I/art     (23546):   0ms/0.977ms (Paused)PausePhase
I/art     (23546):     0.244ms ReMarkRoots
I/art     (23546):     0.672ms (Paused)ScanGrayObjects
I/art     (23546):     0ms (Paused)ProcessMarkStack
I/art     (23546):     0ms/0.610ms SwapStacks
I/art     (23546):       0.610ms RevokeAllThreadLocalAllocationStacks
I/art     (23546):     0ms PreSweepingGcVerification
I/art     (23546):   0ms/10.621ms ReclaimPhase
I/art     (23546):     0.610ms/0.702ms ProcessReferences
I/art     (23546):       0.214ms/0.641ms EnqueueFinalizerReferences
I/art     (23546):         0.427ms ProcessMarkStack
I/art     (23546):     0.488ms SweepSystemWeaks
I/art     (23546):     0.824ms/9.400ms Sweep
I/art     (23546):       0ms SweepMallocSpace
I/art     (23546):       0.214ms SweepZygoteSpace
I/art     (23546):       0.122ms SweepMallocSpace
I/art     (23546):       6.226ms SweepMallocSpace
I/art     (23546):       0ms SweepMallocSpace
I/art     (23546):       2.144ms SweepLargeObjects
I/art     (23546):     0.305ms SwapBitmaps
I/art     (23546):     0ms UnBindBitmaps
I/art     (23546):   0.275ms FinishPhase
I/art     (23546): GC iteration timing logger: end, 178.971ms

Change-Id: Ia55b65609468f212b3cd65cda66b843da42be645
diff --git a/runtime/gc/reference_processor.cc b/runtime/gc/reference_processor.cc
index 292781e..e52bc1f 100644
--- a/runtime/gc/reference_processor.cc
+++ b/runtime/gc/reference_processor.cc
@@ -110,6 +110,7 @@
                                            MarkObjectCallback* mark_object_callback,
                                            ProcessMarkStackCallback* process_mark_stack_callback,
                                            void* arg) {
+  TimingLogger::ScopedTiming t(concurrent ? __FUNCTION__ : "(Paused)ProcessReferences", timings);
   Thread* self = Thread::Current();
   {
     MutexLock mu(self, lock_);
@@ -118,10 +119,9 @@
     process_references_args_.arg_ = arg;
     CHECK_EQ(slow_path_enabled_, concurrent) << "Slow path must be enabled iff concurrent";
   }
-  timings->StartSplit(concurrent ? "ProcessReferences" : "(Paused)ProcessReferences");
   // Unless required to clear soft references with white references, preserve some white referents.
   if (!clear_soft_references) {
-    TimingLogger::ScopedSplit split(concurrent ? "ForwardSoftReferences" :
+    TimingLogger::ScopedTiming split(concurrent ? "ForwardSoftReferences" :
         "(Paused)ForwardSoftReferences", timings);
     if (concurrent) {
       StartPreservingReferences(self);
@@ -138,7 +138,7 @@
   soft_reference_queue_.ClearWhiteReferences(&cleared_references_, is_marked_callback, arg);
   weak_reference_queue_.ClearWhiteReferences(&cleared_references_, is_marked_callback, arg);
   {
-    TimingLogger::ScopedSplit split(concurrent ? "EnqueueFinalizerReferences" :
+    TimingLogger::ScopedTiming t(concurrent ? "EnqueueFinalizerReferences" :
         "(Paused)EnqueueFinalizerReferences", timings);
     if (concurrent) {
       StartPreservingReferences(self);
@@ -173,7 +173,6 @@
       DisableSlowPath(self);
     }
   }
-  timings->EndSplit();
 }
 
 // Process the "referent" field in a java.lang.ref.Reference.  If the referent has not yet been