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

base/trace_event/memory_dump_manager.h

Index: base/trace_event/memory_dump_manager.h
diff --git a/base/trace_event/memory_dump_manager.h b/base/trace_event/memory_dump_manager.h
index e34bdb0853cc6200d3a494969fe8582eb2040f79..9b59b3b49c27b7c6ad71b11d04f5a614a16127ba 100644
--- a/base/trace_event/memory_dump_manager.h
+++ b/base/trace_event/memory_dump_manager.h
@@ -36,6 +36,7 @@ class MemoryDumpSessionState;
 // RequestDumpPoint(). The extension by Un(RegisterDumpProvider).
 class BASE_EXPORT MemoryDumpManager : public TraceLog::EnabledStateObserver {
  public:
+  static const int kInvalidTracingProcessId = -1;
   static const char* const kTraceCategoryForTesting;
 
   static MemoryDumpManager* GetInstance();
@@ -81,6 +82,16 @@ class BASE_EXPORT MemoryDumpManager : public TraceLog::EnabledStateObserver {
     return session_state_;
   }
 
+  // This is used by browser to hash child id to get the tracing_process_id

[Primiano Tucci (use gerrit), 2015/06/24 09:31:00]

Add the following comment here

// Derives a tracing process id from a child process id. Child process ids
// cannot be used directly in tracing for security reasons (see: discussion in
// crrev.com/xxxxxx). This method is meant to be used when dumping cross-process
// shared memory from a process which knows the child process id of its
// endpoints. The value returned by this method is guaranteed to be equal to
// the value returned by tracing_process_id() in the corresponding child
process.

+  // for child.
+  static int ChildProcessIdToTracingProcessId(int child_id);
+
+  int tracing_process_id() const {

[Primiano Tucci (use gerrit), 2015/06/24 09:31:00]

Add a comment saying:

// Returns a unique id for the current process. The id can be retrieved only
// by child processes and only when tracing is enabled. This is intended to 
// express cross-process sharing of memory dumps on the child-process side,
// without having to know the self child process id.

+    // This cannot be requested out of scope of a trace.
+    DCHECK_NE(tracing_process_id_, kInvalidTracingProcessId);
+    return tracing_process_id_;
+  }
+
  private:
   // Descriptor struct used to hold information about registered MDPs. It is
   // deliberately copyable, in order to allow to be used as hash_map value.
@@ -121,6 +132,13 @@ class BASE_EXPORT MemoryDumpManager : public TraceLog::EnabledStateObserver {
       MemoryDumpProvider* mdp,
       scoped_refptr<ProcessMemoryDumpHolder> pmd_holder);
 
+  // Pass kInvalidTracingProcessId for invalidating the id.
+  void set_tracing_process_id(int id) {
+    DCHECK(tracing_process_id_ == kInvalidTracingProcessId ||
+           id == kInvalidTracingProcessId);
+    tracing_process_id_ = id;
+  }
+
   hash_map<MemoryDumpProvider*, MemoryDumpProviderInfo> dump_providers_;
 
   // Shared among all the PMDs to keep state scoped to the tracing session.
@@ -139,6 +157,10 @@ class BASE_EXPORT MemoryDumpManager : public TraceLog::EnabledStateObserver {
   // For time-triggered periodic dumps.
   RepeatingTimer<MemoryDumpManager> periodic_dump_timer_;
 
+  // The unique id of the child process. This is created only for tracing and is
+  // expected to be valid only when tracing is enabled.
+  int tracing_process_id_;
+
   // Skips the auto-registration of the core dumpers during Initialize().
   bool skip_core_dumpers_auto_registration_for_testing_;
 
@@ -165,6 +187,10 @@ class BASE_EXPORT MemoryDumpManagerDelegate {
     MemoryDumpManager::GetInstance()->CreateProcessDump(args, callback);
   }
 
+  void set_tracing_process_id(int id) {
+    MemoryDumpManager::GetInstance()->set_tracing_process_id(id);
+  }
+
  private:
   DISALLOW_COPY_AND_ASSIGN(MemoryDumpManagerDelegate);
 };