[tracing] Dump child processes' memory metrics in browser

base/trace_event/process_memory_totals_dump_provider.h

 // Copyright 2015 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.
 
 #ifndef BASE_TRACE_EVENT_PROCESS_MEMORY_TOTALS_DUMP_PROVIDER_H_
 #define BASE_TRACE_EVENT_PROCESS_MEMORY_TOTALS_DUMP_PROVIDER_H_
 
 #include "base/gtest_prod_util.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/singleton.h"
 #include "base/trace_event/memory_dump_provider.h"
 
 namespace base {
 
 class ProcessMetrics;
 
 namespace trace_event {
 
 // Dump provider which collects process-wide memory stats.
 class BASE_EXPORT ProcessMemoryTotalsDumpProvider : public MemoryDumpProvider {
  public:
-  static ProcessMemoryTotalsDumpProvider* GetInstance();
+  // Creates a dump provider for a child process with |process_id|.
+  // Note: Current Process should be able to access process metrics of the
+  // process, else this method returns empty ptr.
+  static scoped_ptr<ProcessMemoryTotalsDumpProvider> CreateForProcess(
+      ProcessHandle process);
+
+  ~ProcessMemoryTotalsDumpProvider() override;
 
   // MemoryDumpProvider implementation.
   bool OnMemoryDump(const MemoryDumpArgs& args,
                     ProcessMemoryDump* pmd) override;
 
  private:
   friend struct DefaultSingletonTraits<ProcessMemoryTotalsDumpProvider>;
   FRIEND_TEST_ALL_PREFIXES(ProcessMemoryTotalsDumpProviderTest, DumpRSS);
 
   static uint64 rss_bytes_for_testing;
 
-  ProcessMemoryTotalsDumpProvider();
-  ~ProcessMemoryTotalsDumpProvider() override;
+  ProcessMemoryTotalsDumpProvider(ProcessHandle process);
 
+  ProcessHandle process_;
   scoped_ptr<ProcessMetrics> process_metrics_;
 
   DISALLOW_COPY_AND_ASSIGN(ProcessMemoryTotalsDumpProvider);
 };
 
 }  // namespace trace_event
 }  // namespace base
 
 #endif  // BASE_TRACE_EVENT_PROCESS_MEMORY_TOTALS_DUMP_PROVIDER_H_