Persist setup metrics and have Chrome report them during UMA upload.

base/metrics/histogram_persistence.cc

Index: base/metrics/histogram_persistence.cc
diff --git a/base/metrics/histogram_persistence.cc b/base/metrics/histogram_persistence.cc
index 19ca3a2fe9bd6f4dabf1b4e64452c3e058265ba4..1f0c08fe4da228f7bcca3c5a192f8cc389bdd174 100644
--- a/base/metrics/histogram_persistence.cc
+++ b/base/metrics/histogram_persistence.cc
@@ -50,6 +50,9 @@ enum CreateHistogramResultType {
   CREATE_HISTOGRAM_MAX
 };
 
+// Name of histogram for storing results of local operations.
+const char kResultHistogram[] = "UMA.CreatePersistentHistogram.Result";
+
 // Type identifiers used when storing in persistent memory so they can be
 // identified during extraction; the first 4 bytes of the SHA1 of the name
 // is used as a unique integer. A "version number" is added to the base
@@ -149,9 +152,14 @@ HistogramBase* GetCreateHistogramResultHistogram() {
     static bool initialized = false;
     if (!initialized) {
       initialized = true;
+      if (g_allocator) {
+        DLOG(WARNING) << "Creating the results-histogram inside persistent"
+                      << " memory can cause future allocations to crash if"
+                      << " that memory is ever released (for testing).";
+      }
+
       histogram_pointer = LinearHistogram::FactoryGet(
-          "UMA.CreatePersistentHistogram.Result",
-          1, CREATE_HISTOGRAM_MAX, CREATE_HISTOGRAM_MAX + 1,
+          kResultHistogram, 1, CREATE_HISTOGRAM_MAX, CREATE_HISTOGRAM_MAX + 1,
           HistogramBase::kUmaTargetedHistogramFlag);
       base::subtle::Release_Store(
           &atomic_histogram_pointer,
@@ -173,13 +181,7 @@ void SetPersistentHistogramMemoryAllocator(
   // Releasing or changing an allocator is extremely dangerous because it
   // likely has histograms stored within it. If the backing memory is also
   // also released, future accesses to those histograms will seg-fault.
-  // It's not a fatal CHECK() because tests do this knowing that all
-  // such persistent histograms have already been forgotten.
-  if (g_allocator) {
-    LOG(WARNING) << "Active PersistentMemoryAllocator has been released."
-                 << " Some existing histogram pointers may be invalid.";
-    delete g_allocator;
-  }
+  CHECK(!g_allocator);
   g_allocator = allocator;
 }
 
@@ -187,8 +189,35 @@ PersistentMemoryAllocator* GetPersistentHistogramMemoryAllocator() {
   return g_allocator;
 }
 
-PersistentMemoryAllocator* ReleasePersistentHistogramMemoryAllocator() {
+PersistentMemoryAllocator*
+ReleasePersistentHistogramMemoryAllocatorForTesting() {
   PersistentMemoryAllocator* allocator = g_allocator;
+  if (!allocator)
+    return nullptr;
+
+  // Before releasing the memory, it's necessary to have the Statistics
+  // Recorder forget about the histograms contained within otherwise some
+  // operations will try to access it.
+  PersistentMemoryAllocator::Iterator iter;
+  PersistentMemoryAllocator::Reference ref;
+  uint32_t type_id;
+  allocator->CreateIterator(&iter);
+  while ((ref = allocator->GetNextIterable(&iter, &type_id)) != 0) {
+    if (type_id == kTypeIdHistogram) {
+      PersistentHistogramData* histogram_data =
+          allocator->GetAsObject<PersistentHistogramData>(
+              ref, kTypeIdHistogram);
+      DCHECK(histogram_data);
+      std::string name(histogram_data->name);
+      StatisticsRecorder::ForgetHistogramForTesting(name);
+      DLOG(WARNING) << "Dropped persistent histogram \"" << name << "\"";
+
+      // Fix by calling GetCreateHistogramResultHistogram() before setting
+      // the (temporary) persistent memory allocator.
+      DCHECK_NE(kResultHistogram, name);
+    }
+  }
+
   g_allocator = nullptr;
   return allocator;
 };
@@ -444,7 +473,7 @@ HistogramBase* AllocatePersistentHistogram(
 void ImportPersistentHistograms() {
   // The lock protects against concurrent access to the iterator and is created
   // in a thread-safe manner when needed.
-  static base::LazyInstance<base::Lock> lock = LAZY_INSTANCE_INITIALIZER;
+  static base::LazyInstance<base::Lock>::Leaky lock = LAZY_INSTANCE_INITIALIZER;
 
   if (g_allocator) {
     base::AutoLock auto_lock(lock.Get());
@@ -456,7 +485,7 @@ void ImportPersistentHistograms() {
     if (iter.is_clear())
       g_allocator->CreateIterator(&iter);
 
-    for (;;) {
+    while (true) {
       HistogramBase* histogram = GetNextPersistentHistogram(g_allocator, &iter);
       if (!histogram)
         break;