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..3ad25c6d321fe99a07a3e38ce5d88e7cebb6401b 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"
@@ -35,13 +36,30 @@ bool ChildHistogramMessageFilter::OnMessageReceived(
     const IPC::Message& message) {
   bool handled = true;
   IPC_BEGIN_MESSAGE_MAP(ChildHistogramMessageFilter, message)
-    IPC_MESSAGE_HANDLER(ChildProcessMsg_GetChildHistogramData,
+    IPC_MESSAGE_HANDLER(ChildProcessMsg_SetHistogramMemory,
+                        OnSetHistogramMemory)
+    IPC_MESSAGE_HANDLER(ChildProcessMsg_GetChildNonPersistentHistogramData,
                         OnGetChildHistogramData)
     IPC_MESSAGE_UNHANDLED(handled = false)
   IPC_END_MESSAGE_MAP()
   return handled;
 }
 
+void ChildHistogramMessageFilter::OnSetHistogramMemory(
+    const base::SharedMemoryHandle& memory_handle,
+    int memory_size) {
+  // This message must be received only once. Multiple calls to create a global
+  // allocator will cause a CHECK() failure.
+  base::PersistentHistogramAllocator::CreateGlobalAllocatorOnSharedMemoryHandle(
+      memory_handle, memory_size);
+
+  base::PersistentHistogramAllocator* global_allocator =
+      base::PersistentHistogramAllocator::GetGlobalAllocator();
+  if (global_allocator) {

[Alexei Svitkine (slow), 2016/03/31 22:00:58]

Nit: No {}'s

[bcwhite, 2016/03/31 23:53:47]

Done.

+    global_allocator->CreateTrackingHistograms(global_allocator->Name());
+  }
+}
+
 void ChildHistogramMessageFilter::SendHistograms(int sequence_number) {
   io_task_runner_->PostTask(
       FROM_HERE, base::Bind(&ChildHistogramMessageFilter::UploadAllHistograms,