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

content/browser/tracing/tracing_controller_impl.cc

Index: content/browser/tracing/tracing_controller_impl.cc
diff --git a/content/browser/tracing/tracing_controller_impl.cc b/content/browser/tracing/tracing_controller_impl.cc
index e29425f506b61c7c5170b7ed15d49f6937764d9b..a47414a162a1e8ba3c93db708c154c6fab705da8 100644
--- a/content/browser/tracing/tracing_controller_impl.cc
+++ b/content/browser/tracing/tracing_controller_impl.cc
@@ -8,12 +8,14 @@
 #include "base/json/string_escape.h"
 #include "base/macros.h"
 #include "base/strings/string_number_conversions.h"
+#include "base/trace_event/memory_allocator_dump_guid.h"
 #include "base/trace_event/trace_event.h"
 #include "content/browser/tracing/file_tracing_provider_impl.h"
 #include "content/browser/tracing/trace_message_filter.h"
 #include "content/browser/tracing/tracing_ui.h"
 #include "content/common/child_process_messages.h"
 #include "content/public/browser/browser_message_filter.h"
+#include "content/public/common/child_process_host.h"
 #include "content/public/common/content_switches.h"
 
 #if defined(OS_CHROMEOS)
@@ -135,6 +137,9 @@ bool TracingControllerImpl::EnableRecording(
 #endif
   }
 
+  // Set the child process id for the browser process as invalid id.
+  base::trace_event::MemoryAllocatorDumpGuid::SetUniqueChildProcessId(

[Primiano Tucci (use gerrit), 2015/06/19 13:47:50]

It is already invalid above, right? You shouldn't need to call this at all.

[ssid, 2015/06/19 14:51:19]

Hm, I was planning to use maybe 0 for browser process id. But it was useless.
Forgot to remove this.

+      ChildProcessHost::kInvalidUniqueID);
 
   base::Closure on_enable_recording_done_callback =
       base::Bind(&TracingControllerImpl::OnEnableRecordingDone,