Make VEA test support videos with different coded size and visible size

base/files/memory_mapped_file.cc

Index: base/files/memory_mapped_file.cc
diff --git a/base/files/memory_mapped_file.cc b/base/files/memory_mapped_file.cc
index 745a5ff1f4524f944823c244249836b6b52bf9a3..d83792aef282f9aaad34563564f2d4e263bac2e2 100644
--- a/base/files/memory_mapped_file.cc
+++ b/base/files/memory_mapped_file.cc
@@ -35,7 +35,9 @@ bool MemoryMappedFile::Initialize(const FilePath& file_name) {
   if (IsValid())
     return false;
 
-  file_.Initialize(file_name, File::FLAG_OPEN | File::FLAG_READ);
+  file_.Initialize(file_name, File::FLAG_OPEN |
+                              File::FLAG_READ |
+                              File::FLAG_WRITE);
 
   if (!file_.IsValid()) {
     DLOG(ERROR) << "Couldn't open " << file_name.AsUTF8Unsafe();