Add crash keys about field trial shared memory errors.

base/metrics/field_trial.cc

Index: base/metrics/field_trial.cc
diff --git a/base/metrics/field_trial.cc b/base/metrics/field_trial.cc
index 78602f1e613d39f00020dea6f1f18f093bcfa72f..9a0121635830b943057e40a9eece6fa35ee74ca8 100644
--- a/base/metrics/field_trial.cc
+++ b/base/metrics/field_trial.cc
@@ -11,6 +11,7 @@
 #include "base/build_time.h"
 #include "base/command_line.h"
 #include "base/debug/activity_tracker.h"
+#include "base/debug/crash_logging.h"
 #include "base/logging.h"
 #include "base/metrics/field_trial_param_associator.h"
 #include "base/process/memory.h"
@@ -1230,11 +1231,25 @@ void FieldTrialList::InstantiateFieldTrialAllocatorIfNeeded() {
 #endif
 
   std::unique_ptr<SharedMemory> shm(new SharedMemory());
-  if (!shm->Create(options))
+  if (!shm->Create(options)) {
+#if !defined(OS_NACL)
+    // Temporary for http://crbug.com/703649.
+    base::debug::ScopedCrashKey crash_key(
+        "field_trial_shmem_create_error",
+        base::IntToString(static_cast<int>(shm->get_last_error())));
+#endif
     OnOutOfMemory(kFieldTrialAllocationSize);
+  }
 
-  if (!shm->Map(kFieldTrialAllocationSize))
+  if (!shm->Map(kFieldTrialAllocationSize)) {
+#if !defined(OS_NACL)
+    // Temporary for http://crbug.com/703649.
+    base::debug::ScopedCrashKey crash_key(
+        "field_trial_shmem_map_error",
+        base::IntToString(static_cast<int>(shm->get_last_error())));
+#endif
     OnOutOfMemory(kFieldTrialAllocationSize);
+  }
 
   global_->field_trial_allocator_.reset(
       new FieldTrialAllocator(std::move(shm), 0, kAllocatorName, false));