Fix more disabled MSVC warnings, base/ edition.

Mostly this fixes cases of "possible value truncation", usually by inserting
explicit typecasts.

BUG=81439
TEST=none

Review URL: https://codereview.chromium.org/596103002

Cr-Commit-Position: refs/heads/master@{#297723}
diff --git a/base/logging_win.cc b/base/logging_win.cc
index a3c3a5b..53cc37c 100644
--- a/base/logging_win.cc
+++ b/base/logging_win.cc
@@ -44,7 +44,7 @@
         break;
     }
   } else {  // severity < 0 is VLOG verbosity levels.
-    level = TRACE_LEVEL_INFORMATION - severity;
+    level = static_cast<EtwEventLevel>(TRACE_LEVEL_INFORMATION - severity);
   }
 
   // Bail if we're not logging, not at that level,