[HttpCache] Store some memcache info to memory dumps for debugging

net/disk_cache/memory/mem_backend_impl.cc

Index: net/disk_cache/memory/mem_backend_impl.cc
diff --git a/net/disk_cache/memory/mem_backend_impl.cc b/net/disk_cache/memory/mem_backend_impl.cc
index 65e14d71686da03b3c1fd36b58a91024837f4cb1..bae32910735483b79ac7f662a84567be7206ff19 100644
--- a/net/disk_cache/memory/mem_backend_impl.cc
+++ b/net/disk_cache/memory/mem_backend_impl.cc
@@ -12,6 +12,7 @@
 #include "base/memory/ptr_util.h"
 #include "base/sys_info.h"
 #include "base/trace_event/memory_usage_estimator.h"
+#include "base/trace_event/process_memory_dump.h"
 #include "net/base/net_errors.h"
 #include "net/disk_cache/cache_util.h"
 #include "net/disk_cache/memory/mem_entry_impl.h"
@@ -284,11 +285,29 @@ void MemBackendImpl::OnExternalCacheHit(const std::string& key) {
     it->second->UpdateStateOnUse(MemEntryImpl::ENTRY_WAS_NOT_MODIFIED);
 }
 
-size_t MemBackendImpl::EstimateMemoryUsage() const {
+size_t MemBackendImpl::DumpMemoryStats(
+    base::trace_event::ProcessMemoryDump* pmd,
+    const std::string& parent_absolute_name) const {
+  base::trace_event::MemoryAllocatorDump* dump =
+      pmd->CreateAllocatorDump(parent_absolute_name + "/memory_backend");
+
   // Entries in lru_list_ will be counted by EMU but not in entries_ since
   // they're pointers.
-  return base::trace_event::EstimateMemoryUsage(lru_list_) +
-         base::trace_event::EstimateMemoryUsage(entries_);
+  size_t size = base::trace_event::EstimateMemoryUsage(lru_list_) +
+                base::trace_event::EstimateMemoryUsage(entries_);
+  dump->AddScalar(base::trace_event::MemoryAllocatorDump::kNameSize,
+                  base::trace_event::MemoryAllocatorDump::kUnitsBytes, size);
+
+  dump->AddScalar("phys_mem",
+                  base::trace_event::MemoryAllocatorDump::kUnitsBytes,
+                  base::SysInfo::AmountOfPhysicalMemory());

[ssid, 2017/03/27 18:59:42]

Um, we already have this data from the crash server and dashboard. I can help
you get this information if you need.
Any reason why we add this here?

[jkarlin, 2017/03/28 15:09:45]

I've removed it, but are you 100% certain that the dashboard and crash server
are getting their value with the same API?

+  dump->AddScalar("cur_size",
+                  base::trace_event::MemoryAllocatorDump::kUnitsBytes,

[ssid, 2017/03/27 18:59:42]

I'd make these names as current_size and system_physical_size. Reason: the
tracing is used by everyone, not juts for debugging and descriptive names are
better for users.
Unfortunately these 2 are coupled in memory-infra.

[jkarlin, 2017/03/28 15:09:45]

Done.

+                  current_size_);
+  dump->AddScalar("max_size",
+                  base::trace_event::MemoryAllocatorDump::kUnitsBytes,
+                  max_size_);
+  return size;
 }
 
 void MemBackendImpl::EvictIfNeeded() {