windows: Fix a few things clang complains about.

base/allocator/allocator_shim.cc

Index: base/allocator/allocator_shim.cc
diff --git a/base/allocator/allocator_shim.cc b/base/allocator/allocator_shim.cc
index 97bbf90c63e5e7b1f88ca1b37ab7e8d73b6e885f..a76f8a34cf19daff98d87ff209bfeb58c0ac54ff 100644
--- a/base/allocator/allocator_shim.cc
+++ b/base/allocator/allocator_shim.cc
@@ -294,7 +294,7 @@ void SetupSubprocessAllocator() {
   buffer[sizeof(buffer) - 1] = '\0';
 
   if (secondary_length || !primary_length) {
-    char* secondary_value = secondary_length ? buffer : "TCMALLOC";
+    const char* secondary_value = secondary_length ? buffer : "TCMALLOC";
     // Force renderer (or other subprocesses) to use secondary_value.
     int ret_val = _putenv_s(primary_name, secondary_value);
     DCHECK_EQ(0, ret_val);