Fix PP_FileOpenFlags_Dev handling:

base/platform_file_posix.cc

Index: base/platform_file_posix.cc
diff --git a/base/platform_file_posix.cc b/base/platform_file_posix.cc
index 2ffac06456aac130f20622b0547319fec99bf3f1..a1388d6c3a426f462b46b57c39e521a6019272e4 100644
--- a/base/platform_file_posix.cc
+++ b/base/platform_file_posix.cc
@@ -44,6 +44,12 @@ PlatformFile CreatePlatformFile(const FilePath& name, int flags,
     open_flags = O_CREAT | O_TRUNC;
   }
 
+  if (flags & PLATFORM_FILE_OPEN_TRUNCATED) {
+    DCHECK(!open_flags);
+    DCHECK(flags & PLATFORM_FILE_WRITE);
+    open_flags = O_TRUNC;
+  }
+
   if (!open_flags && !(flags & PLATFORM_FILE_OPEN) &&
       !(flags & PLATFORM_FILE_OPEN_ALWAYS)) {
     NOTREACHED();
@@ -62,11 +68,6 @@ PlatformFile CreatePlatformFile(const FilePath& name, int flags,
     NOTREACHED();
   }
 
-  if (flags & PLATFORM_FILE_TRUNCATE) {
-    DCHECK(flags & PLATFORM_FILE_WRITE);
-    open_flags |= O_TRUNC;
-  }
-
   COMPILE_ASSERT(O_RDONLY == 0, O_RDONLY_must_equal_zero);
 
   int descriptor =