Adjust memory sizes of persistent histogram allocations.

content/browser/renderer_host/render_process_host_impl.cc

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Represents the browser side of the browser <--> renderer communication
 // channel. There will be one RenderProcessHost per renderer process.
 
 #include "content/browser/renderer_host/render_process_host_impl.h"
 
 #include <algorithm>
@@ skipping 2579 matching lines @@
 
   // Get handle to the renderer process. Stop if there is none.
   base::ProcessHandle destination = GetHandle();
   if (destination == base::kNullProcessHandle)
     return;
 
   // If a renderer crashes before completing startup and gets restarted, this
   // method will get called a second time meaning that a metrics-allocator
   // already exists. Don't recreate it.
   if (!metrics_allocator_) {
-    // TODO(bcwhite): Update this with the correct memory size.
+    // Create persistent/shared memory and allow histograms to be stored in
+    // it. Memory that is not actualy used won't be physically mapped by the
+    // system. RendererMetrics usage, as reported in UMA, peaked around 0.7MiB
+    // as of 2016-12-20.
     std::unique_ptr<base::SharedMemory> shm(new base::SharedMemory());
     if (!shm->CreateAndMapAnonymous(2 << 20))  // 2 MiB
       return;
     metrics_allocator_.reset(new base::SharedPersistentMemoryAllocator(
         std::move(shm), GetID(), "RendererMetrics", /*readonly=*/false));
   }
 
   base::SharedMemoryHandle shm_handle;
   metrics_allocator_->shared_memory()->ShareToProcess(destination, &shm_handle);
   Send(new ChildProcessMsg_SetHistogramMemory(
@@ skipping 386 matching lines @@
   LOG(ERROR) << "Terminating render process for bad Mojo message: " << error;
 
   // The ReceivedBadMessage call below will trigger a DumpWithoutCrashing. Alias
   // enough information here so that we can determine what the bad message was.
   base::debug::Alias(&error);
   bad_message::ReceivedBadMessage(render_process_id,
                                   bad_message::RPH_MOJO_PROCESS_ERROR);
 }
 
 }  // namespace content