[tracing] Display the resident size of the discardable memory segments

base/trace_event/process_memory_dump.h

Index: base/trace_event/process_memory_dump.h
diff --git a/base/trace_event/process_memory_dump.h b/base/trace_event/process_memory_dump.h
index da18a14b1ca1d2909224011fcb5bc89d0286b69e..8d37ba7a010d3c251ee8be459ab59279d5a863ee 100644
--- a/base/trace_event/process_memory_dump.h
+++ b/base/trace_event/process_memory_dump.h
@@ -41,6 +41,12 @@ class BASE_EXPORT ProcessMemoryDump {
   using AllocatorDumpsMap =
       SmallMap<hash_map<std::string, MemoryAllocatorDump*>>;
 
+  // Returns the total bytes resident for a memory segment, with given
+  // |start_address| and |mapped_size|. |mapped_size| is specified in bytes. The
+  // value returned is valid only if the given range is currently mmapped by the
+  // process. Returns -1 if counting is not implemented in the current platform.

[reveman, 2015/10/07 09:40:04]

Can we have a IsCountResidentBytesSupported() function instead of using a
negative return value for when this is not supported on a platform? Or maybe
even better, #ifdef the function so it's only compiled and available on
platforms where this is supported.

+  static int64 CountResidentBytes(void* start_address, size_t mapped_size);
+
   ProcessMemoryDump(const scoped_refptr<MemoryDumpSessionState>& session_state);
   ~ProcessMemoryDump();