Pass the GUID for the SharedMemoryHandle used by base::FieldTrialList.

base/metrics/field_trial.h

Index: base/metrics/field_trial.h
diff --git a/base/metrics/field_trial.h b/base/metrics/field_trial.h
index 60a6592ce617a220cf6c6d1fb65936f6876b2fcf..d36a47c434dd922f4d7674fdb878081d1d34bcb5 100644
--- a/base/metrics/field_trial.h
+++ b/base/metrics/field_trial.h
@@ -72,6 +72,7 @@
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/shared_memory.h"
+#include "base/memory/shared_memory_handle.h"
 #include "base/metrics/persistent_memory_allocator.h"
 #include "base/observer_list_threadsafe.h"
 #include "base/pickle.h"
@@ -573,9 +574,9 @@ class BASE_EXPORT FieldTrialList {
 
 #if defined(OS_POSIX) && !defined(OS_NACL)
   // On POSIX, we also need to explicitly pass down this file descriptor that
-  // should be shared with the child process. Returns kInvalidPlatformFile if no
-  // handle exists or was not initialized properly.
-  static PlatformFile GetFieldTrialHandle();
+  // should be shared with the child process. Returns an invalid handle if it
+  // was not initialized properly.
+  static base::SharedMemoryHandle GetFieldTrialHandle();
 #endif
 
   // Adds a switch to the command line containing the field trial state as a
@@ -645,19 +646,37 @@ class BASE_EXPORT FieldTrialList {
                            DoNotAddSimulatedFieldTrialsToAllocator);
   FRIEND_TEST_ALL_PREFIXES(FieldTrialListTest, AssociateFieldTrialParams);
   FRIEND_TEST_ALL_PREFIXES(FieldTrialListTest, ClearParamsFromSharedMemory);
+  FRIEND_TEST_ALL_PREFIXES(FieldTrialListTest,
+                           SerializeSharedMemoryHandleMetadata);
+
+  // Serialization and deserialization doesn't actually transport the underlying

[Alexei Svitkine (slow), 2017/05/05 18:02:16]

Please start this comment explaining what serialization/deserialization is for
(i.e. used to tell child processes about the segment). The current comment you
have makes sense as a second sentence.

[erikchen, 2017/05/05 19:41:51]

Done.

+  // OS resource - that must be done by the Process launcher.
+  static std::string SerializeSharedMemoryHandleMetadata(
+      const SharedMemoryHandle& shm);
+#if defined(OS_WIN)
+  static SharedMemoryHandle DeserializeSharedMemoryHandleMetadata(
+      const std::string& switch_value);
+#elif defined(OS_POSIX) && !defined(OS_NACL)
+  static SharedMemoryHandle DeserializeSharedMemoryHandleMetadata(
+      int fd,
+      const std::string& switch_value);
+#endif
 
 #if defined(OS_WIN)
   // Takes in |handle_switch| from the command line which represents the shared
   // memory handle for field trials, parses it, and creates the field trials.
   // Returns true on success, false on failure.
-  static bool CreateTrialsFromHandleSwitch(const std::string& handle_switch);
+  // |switch_value| also contains the serialized GUID.
+  static bool CreateTrialsFromSwitchValue(const std::string& switch_value);
 #endif
 
 #if defined(OS_POSIX) && !defined(OS_NACL)
   // On POSIX systems that use the zygote, we look up the correct fd that backs
   // the shared memory segment containing the field trials by looking it up via
   // an fd key in GlobalDescriptors. Returns true on success, false on failure.
-  static bool CreateTrialsFromDescriptor(int fd_key);
+  // |switch_value| also contains the serialized GUID.
+  static bool CreateTrialsFromDescriptor(int fd_key,
+                                         const std::string& switch_value);
 #endif
 
   // Takes an unmapped SharedMemoryHandle, creates a SharedMemory object from it
@@ -731,7 +750,7 @@ class BASE_EXPORT FieldTrialList {
   // Readonly copy of the handle to the allocator. Needs to be a member variable
   // because it's needed from both CopyFieldTrialStateToFlags() and
   // AppendFieldTrialHandleIfNeeded().
-  PlatformFile readonly_allocator_handle_ = kInvalidPlatformFile;
+  base::SharedMemoryHandle readonly_allocator_handle_;
 
   // Tracks whether CreateTrialsFromCommandLine() has been called.
   bool create_trials_from_command_line_called_ = false;