Fix enum vs unsigned -Wsign-compare warnings

Recent Clang versions started taking into account that enums are signed
on Windows when emitting these warnings.

TBR=jochen

Bug: 792519
Change-Id: If9fdc280b0d6a79105e9191a18214077565dcddb
Reviewed-on: https://chromium-review.googlesource.com/816045
Reviewed-by: Hans Wennborg <hans@chromium.org>
Commit-Queue: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522673}

chrome/installer/util/l10n_string_util_unittest.cc

@@ -69,7 +69,8 @@ TEST(GetBaseMessageIdForMode, GoogleStringIds) {
 
   // Run through all install modes, checking that the mode-specific strings are
   // mapped properly by GetBaseMessageIdForMode.
-  ASSERT_EQ(install_static::NUM_INSTALL_MODES, mode_to_strings.size());
+  ASSERT_EQ(static_cast<size_t>(install_static::NUM_INSTALL_MODES),
+            mode_to_strings.size());
   for (int mode_index = 0; mode_index < install_static::NUM_INSTALL_MODES;
        ++mode_index) {
     SCOPED_TRACE(testing::Message() << "install mode index: " << mode_index);

media/formats/mp4/box_reader_unittest.cc

@@ -100,7 +100,7 @@ class BoxReaderTest : public testing::Test {
 
     EXPECT_EQ(result, ParseResult::kOk);
     EXPECT_TRUE(reader);
-    EXPECT_EQ(fourCC, reader->type());
+    EXPECT_EQ(fourCC, static_cast<uint32_t>(reader->type()));
     EXPECT_EQ(reader->box_size(), data_size);
   }