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

content/child/child_histogram_message_filter.cc

Index: content/child/child_histogram_message_filter.cc
diff --git a/content/child/child_histogram_message_filter.cc b/content/child/child_histogram_message_filter.cc
index f749cf812fb571c502af103b8068c53b71aeb271..eacec3bb2f39e1af179371a4a9aa186b0c94f5a5 100644
--- a/content/child/child_histogram_message_filter.cc
+++ b/content/child/child_histogram_message_filter.cc
@@ -9,6 +9,7 @@
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/metrics/histogram_delta_serialization.h"
+#include "base/metrics/persistent_histogram_allocator.h"
 #include "base/single_thread_task_runner.h"
 #include "content/child/child_process.h"
 #include "content/common/child_process_messages.h"
@@ -35,6 +36,8 @@ bool ChildHistogramMessageFilter::OnMessageReceived(
     const IPC::Message& message) {
   bool handled = true;
   IPC_BEGIN_MESSAGE_MAP(ChildHistogramMessageFilter, message)
+    IPC_MESSAGE_HANDLER(ChildProcessMsg_SetHistogramMemory,
+                        OnSetHistogramMemory)
     IPC_MESSAGE_HANDLER(ChildProcessMsg_GetChildHistogramData,
                         OnGetChildHistogramData)
     IPC_MESSAGE_UNHANDLED(handled = false)
@@ -42,6 +45,19 @@ bool ChildHistogramMessageFilter::OnMessageReceived(
   return handled;
 }
 
+void ChildHistogramMessageFilter::OnSetHistogramMemory(
+    const base::SharedMemoryHandle& mem_handle,

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

Nit: memory_handle and memory_size

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

Done.

+    int mem_size) {
+  base::PersistentHistogramAllocator::CreateGlobalAllocatorOnSharedMemoryHandle(
+      mem_handle, mem_size);
+
+  base::PersistentHistogramAllocator* global_allocator =
+      base::PersistentHistogramAllocator::GetGlobalAllocator();
+  if (global_allocator) {
+    global_allocator->CreateTrackingHistograms(global_allocator->Name());
+  }
+}
+
 void ChildHistogramMessageFilter::SendHistograms(int sequence_number) {
   io_task_runner_->PostTask(
       FROM_HERE, base::Bind(&ChildHistogramMessageFilter::UploadAllHistograms,