Use correctly-typed error codes for fx_codec_jpx_unittest

Needed to fix the failed pdfium_unittests on windows.  Ironically,
I created these constants so I wouldn't mix up size_t's and off_t's
in these tests, but I didn't apply them consistently.

R=thestig@chromium.org

Review URL: https://codereview.chromium.org/1036743005
diff --git a/core/src/fxcodec/codec/fx_codec_jpx_unittest.cpp b/core/src/fxcodec/codec/fx_codec_jpx_unittest.cpp
index f867788..3e16bd0 100644
--- a/core/src/fxcodec/codec/fx_codec_jpx_unittest.cpp
+++ b/core/src/fxcodec/codec/fx_codec_jpx_unittest.cpp
@@ -45,16 +45,16 @@
     EXPECT_EQ(0xbd, buffer[0]);
 
     // writes of size 0 do nothing but return an error code.
-    EXPECT_EQ(kReadError, opj_write_from_memory(buffer, 0, &dd));
+    EXPECT_EQ(kWriteError, opj_write_from_memory(buffer, 0, &dd));
 
     // writes of nonzero size do nothing but return an error code.
-    EXPECT_EQ(kReadError, opj_write_from_memory(buffer, sizeof(buffer), &dd));
+    EXPECT_EQ(kWriteError, opj_write_from_memory(buffer, sizeof(buffer), &dd));
 
     // Skips of size 0 always return an error code.
-    EXPECT_EQ(kReadError, opj_skip_from_memory(0, &dd));
+    EXPECT_EQ(kSkipError, opj_skip_from_memory(0, &dd));
 
     // Skips of nonzero size always return an error code.
-    EXPECT_EQ(kReadError, opj_skip_from_memory(1, &dd));
+    EXPECT_EQ(kSkipError, opj_skip_from_memory(1, &dd));
 
     // Seeks to 0 offset return in error.
     EXPECT_FALSE(opj_seek_from_memory(0, &dd));
@@ -78,16 +78,16 @@
     EXPECT_EQ(0xbd, buffer[0]);
 
     // writes of size 0 do nothing but return an error code.
-    EXPECT_EQ(kReadError, opj_write_from_memory(buffer, 0, &dd));
+    EXPECT_EQ(kWriteError, opj_write_from_memory(buffer, 0, &dd));
 
     // writes of nonzero size do nothing but return an error code.
-    EXPECT_EQ(kReadError, opj_write_from_memory(buffer, sizeof(buffer), &dd));
+    EXPECT_EQ(kWriteError, opj_write_from_memory(buffer, sizeof(buffer), &dd));
 
     // Skips of size 0 always return an error code.
-    EXPECT_EQ(kReadError, opj_skip_from_memory(0, &dd));
+    EXPECT_EQ(kSkipError, opj_skip_from_memory(0, &dd));
 
     // Skips of nonzero size always return an error code.
-    EXPECT_EQ(kReadError, opj_skip_from_memory(1, &dd));
+    EXPECT_EQ(kSkipError, opj_skip_from_memory(1, &dd));
 
     // Seeks to 0 offset return in error.
     EXPECT_FALSE(opj_seek_from_memory(0, &dd));