[NaCl SDK] A bunch of spelling fixes.

native_client_sdk/src/libraries/nacl_io_test/mount_test.cc

 /* Copyright (c) 2012 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include <errno.h>
 #include <fcntl.h>
 #include <string.h>
 #include <string>
 #include <sys/stat.h>
@@ skipping 38 matching lines @@
 TEST(MountTest, Sanity) {
   MountMemMock* mnt = new MountMemMock();
   MountNode* file;
   MountNode* root;
 
   char buf1[1024];
 
   // A memory mount starts with one directory node: the root.
   EXPECT_EQ(1, mnt->num_nodes());
 
-  // Fail to open non existant file
+  // Fail to open non existent file
   EXPECT_EQ(NULL_NODE, mnt->Open(Path("/foo"), O_RDWR));
   EXPECT_EQ(errno, ENOENT);
 
   // Create a file
   file =  mnt->Open(Path("/foo"), O_RDWR | O_CREAT);
   EXPECT_NE(NULL_NODE, file);
   if (file == NULL) return;
   EXPECT_EQ(2, file->RefCount());
   EXPECT_EQ(2, mnt->num_nodes());
 
@@ skipping 148 matching lines @@
   double expected_count = kTotalSamples / 256.;
   double chi_squared = 0;
   for (int i = 0; i < 256; ++i) {
     double difference = byte_count[i] - expected_count;
     chi_squared += difference * difference / expected_count;
   }
 
   // Approximate chi-squared value for p-value 0.05, 255 degrees-of-freedom.
   EXPECT_LE(chi_squared, 293.24);
 }