Implement MojoGetBufferInformation(), part 1.

mojo/edk/system/dispatcher.cc

Index: mojo/edk/system/dispatcher.cc
diff --git a/mojo/edk/system/dispatcher.cc b/mojo/edk/system/dispatcher.cc
index de2af7d143c0e2a9f99d0a0fdc1ce6308c325c2a..f6bc98eb2f26629c9073ec29958a4af329c50b7c 100644
--- a/mojo/edk/system/dispatcher.cc
+++ b/mojo/edk/system/dispatcher.cc
@@ -206,6 +206,16 @@ MojoResult Dispatcher::DuplicateBufferHandle(
   return DuplicateBufferHandleImplNoLock(options, new_dispatcher);
 }
 
+MojoResult Dispatcher::GetBufferInformation(
+    UserPointer<MojoBufferInformation> info,
+    uint32_t info_num_bytes) {
+  MutexLocker locker(&mutex_);
+  if (is_closed_)
+    return MOJO_RESULT_INVALID_ARGUMENT;
+
+  return GetBufferInformationImplNoLock(info, info_num_bytes);
+}
+
 MojoResult Dispatcher::MapBuffer(
     uint64_t offset,
     uint64_t num_bytes,
@@ -358,6 +368,15 @@ MojoResult Dispatcher::DuplicateBufferHandleImplNoLock(
   return MOJO_RESULT_INVALID_ARGUMENT;
 }
 
+MojoResult Dispatcher::GetBufferInformationImplNoLock(
+    UserPointer<MojoBufferInformation> /*info*/,
+    uint32_t /*info_num_bytes*/) {
+  mutex_.AssertHeld();
+  DCHECK(!is_closed_);
+  // By default, not supported. Only needed for buffer dispatchers.
+  return MOJO_RESULT_INVALID_ARGUMENT;
+}
+
 MojoResult Dispatcher::MapBufferImplNoLock(
     uint64_t /*offset*/,
     uint64_t /*num_bytes*/,