[tracing] Send unique tracing process id for cross-process memory dumps identification.

base/trace_event/memory_dump_manager.cc

Index: base/trace_event/memory_dump_manager.cc
diff --git a/base/trace_event/memory_dump_manager.cc b/base/trace_event/memory_dump_manager.cc
index 3814c21fd28698babd28008c41ca85283b3e817f..a184cdcb77836fd17c8306d0deb1235e4a262b9e 100644
--- a/base/trace_event/memory_dump_manager.cc
+++ b/base/trace_event/memory_dump_manager.cc
@@ -157,6 +157,7 @@ void MemoryDumpManager::SetInstanceForTesting(MemoryDumpManager* instance) {
 MemoryDumpManager::MemoryDumpManager()
     : delegate_(nullptr),
       memory_tracing_enabled_(0),
+      tracing_process_id_(kInvalidTracingProcessId),
       skip_core_dumpers_auto_registration_for_testing_(false) {
   g_next_guid.GetNext();  // Make sure that first guid is not zero.
 }
@@ -432,6 +433,11 @@ void MemoryDumpManager::OnTraceLogDisabled() {
   session_state_ = nullptr;
 }
 
+// static
+int MemoryDumpManager::ChildProcessIdToTracingProcessId(int child_process_id) {
+  return 1000 + child_process_id;

[picksi, 2015/06/24 11:12:43]

Can we use a named const to explain the 1000, e.g. 'kPreventIDAliasingOffset'
... or whatever it is.

[jam, 2015/06/24 16:38:15]

why is this guessable? i.e. why not a hash?

[Primiano Tucci (use gerrit), 2015/06/24 17:47:34]

+1

+}
+
 MemoryDumpManager::MemoryDumpProviderInfo::MemoryDumpProviderInfo(
     const scoped_refptr<SingleThreadTaskRunner>& task_runner)
     : task_runner(task_runner), consecutive_failures(0), disabled(false) {