Create and pass shared-histogram-allocator from browser to renderer.

base/metrics/persistent_histogram_allocator.cc

Index: base/metrics/persistent_histogram_allocator.cc
diff --git a/base/metrics/persistent_histogram_allocator.cc b/base/metrics/persistent_histogram_allocator.cc
index 6006d31fbee70031acb901fb6a0f04a944f5ff04..efa4fa8e436aa53ea8070eb93f24a3c2b7049466 100644
--- a/base/metrics/persistent_histogram_allocator.cc
+++ b/base/metrics/persistent_histogram_allocator.cc
@@ -7,6 +7,7 @@
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/memory/shared_memory.h"
 #include "base/metrics/histogram.h"
 #include "base/metrics/histogram_base.h"
 #include "base/metrics/histogram_samples.h"
@@ -255,14 +256,34 @@ void PersistentHistogramAllocator::CreateGlobalAllocatorOnLocalMemory(
 
 // static
 void PersistentHistogramAllocator::CreateGlobalAllocatorOnSharedMemory(
+    scoped_ptr<SharedMemory> memory,
     size_t size,
-    const SharedMemoryHandle& handle) {
+    uint64_t id,
+    StringPiece name) {
+  if (!memory->memory()) {
+    if (!memory->Map(size))

[Alexei Svitkine (slow), 2016/03/29 17:51:24]

Nit: Combine with the above if and then remove {}'s

[bcwhite, 2016/03/30 21:25:55]

Done.

+      NOTREACHED();
+  }
+
+  if (memory->memory()) {
+    DCHECK_LE(memory->mapped_size(), size);
+    SetGlobalAllocator(make_scoped_ptr(new PersistentHistogramAllocator(
+        make_scoped_ptr(new SharedPersistentMemoryAllocator(
+            std::move(memory), id, name, /*readonly=*/false)))));
+  }
+}
+
+// static
+void PersistentHistogramAllocator::CreateGlobalAllocatorOnSharedMemoryHandle(
+    const SharedMemoryHandle& handle,
+    size_t size) {
   scoped_ptr<SharedMemory> shm(new SharedMemory(handle, /*readonly=*/false));
   if (!shm->Map(size)) {
     NOTREACHED();
     return;
   }
 
+  DCHECK_LE(shm->mapped_size(), size);
   SetGlobalAllocator(make_scoped_ptr(new PersistentHistogramAllocator(
       make_scoped_ptr(new SharedPersistentMemoryAllocator(
           std::move(shm), 0, StringPiece(), /*readonly=*/false)))));