Add crash keys about field trial shared memory errors.

base/memory/shared_memory.h

Index: base/memory/shared_memory.h
diff --git a/base/memory/shared_memory.h b/base/memory/shared_memory.h
index 9d8fd5c3d9fa89030faa450434c9237b9bb2c997..872c38a4798a44a3a67f2200a581b2fbde48310d 100644
--- a/base/memory/shared_memory.h
+++ b/base/memory/shared_memory.h
@@ -64,6 +64,22 @@ struct BASE_EXPORT SharedMemoryCreateOptions {
   bool share_read_only = false;
 };
 
+// Enumeration of different shared memory error types. Note: Currently only
+// errors from Mac POSIX shared memory implementation are fully instrumented.
+// TODO(asvitkine): Evaluate whether we want to keep this ability after
+// crbug.com/703649 is fixed and expand to all platforms or remove.
+enum class SharedMemoryError {
+  NO_ERRORS,
+  NO_FILE,
+  BAD_PARAMS,
+  STAT_FAILED,
+  TRUNCATE_FAILED,
+  NO_TEMP_DIR,
+  MAKE_READONLY_FAILED,
+  INODE_MISMATCH,
+  MMAP_FAILED,
+};
+
 // Platform abstraction for shared memory.
 // SharedMemory consumes a SharedMemoryHandle [potentially one that it created]
 // to map a shared memory OS resource into the virtual address space of the
@@ -233,6 +249,13 @@ class BASE_EXPORT SharedMemory {
   bool GetUniqueId(UniqueId* id) const;
 #endif
 
+  // Returns the last error encountered as a result of a call to Create() or
+  // Map(). Note: Currently only errors from Mac POSIX shared memory
+  // implementation are fully instrumented.
+  // TODO(asvitkine): Evaluate whether we want to keep this ability after
+  // crbug.com/703649 is fixed and expand to all platforms or remove.
+  SharedMemoryError get_last_error() const { return last_error_; }
+
  private:
 #if defined(OS_POSIX) && !defined(OS_NACL) && !defined(OS_ANDROID) && \
     (!defined(OS_MACOSX) || defined(OS_IOS))
@@ -263,6 +286,7 @@ class BASE_EXPORT SharedMemory {
   void* memory_ = nullptr;
   bool read_only_ = false;
   size_t requested_size_ = 0;
+  SharedMemoryError last_error_ = SharedMemoryError::NO_ERRORS;
 
   DISALLOW_COPY_AND_ASSIGN(SharedMemory);
 };