tests: fix a few msvc warnings

Change-Id: I7ee89d6fc2afc20563d1784598ce83e29c0e6651

test/i420_video_source.h

@@ -52,7 +52,7 @@ class I420VideoSource : public VideoSource {
     ASSERT_TRUE(input_file_ != NULL) << "Input file open failed. Filename: "
         << file_name_;
     if (start_) {
-      fseek(input_file_, raw_sz_ * start_, SEEK_SET);
+      fseek(input_file_, static_cast<unsigned>(raw_sz_) * start_, SEEK_SET);
     }
 
     frame_ = start_;

test/subtract_test.cc

@@ -59,7 +59,7 @@ TEST_P(SubtractBlockTest, SimpleSubtract) {
     int16_t *src_diff = be.src_diff;
     for (int r = 0; r < kBlockHeight; ++r) {
       for (int c = 0; c < kBlockWidth; ++c) {
-        src_diff[c] = static_cast<int16_t>(0xa5a5);
+        src_diff[c] = static_cast<int16_t>(0xa5a5u);
       }
       src_diff += kDiffPredStride;
     }

test/test_vector_test.cc

@@ -35,7 +35,7 @@ class TestVectorTest : public ::libvpx_test::DecoderTest,
 
   void OpenMD5File(const std::string& md5_file_name_) {
     md5_file_ = libvpx_test::OpenTestDataFile(md5_file_name_);
-    ASSERT_TRUE(md5_file_) << "Md5 file open failed. Filename: "
+    ASSERT_TRUE(md5_file_ != NULL) << "Md5 file open failed. Filename: "
         << md5_file_name_;
   }
 

test/vp8_boolcoder_test.cc

@@ -43,7 +43,7 @@ void encrypt_buffer(uint8_t *buffer, int size) {
 
 void test_decrypt_cb(void *decrypt_state, const uint8_t *input,
                            uint8_t *output, int count) {
-  int offset = input - reinterpret_cast<uint8_t *>(decrypt_state);
+  const size_t offset = input - reinterpret_cast<uint8_t*>(decrypt_state);
   for (int i = 0; i < count; i++) {
     output[i] = input[i] ^ secret_key[(offset + i) & 15];
   }