Fixes for re-enabling more MSVC level 4 warnings: misc edition #2

This contains fixes for the following sorts of issues:
* Assignment inside conditional
* Taking the address of a temporary
* Octal escape sequence terminated by decimal number
* Signedness mismatch
* Possibly-uninitialized local variable

This also contains a small number of cleanups to nearby code (e.g. no else after return).

BUG=81439
TEST=none

Review URL: https://codereview.chromium.org/382673002

Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 481c3e82e2dcbcb676501f18bc8f58900071b935

tools/gn/tokenizer.cc

diff --git a/tools/gn/tokenizer.cc b/tools/gn/tokenizer.cc
index c089006..87a4d90 100644
--- a/tools/gn/tokenizer.cc
+++ b/tools/gn/tokenizer.cc
@@ -134,14 +134,13 @@
 
 // static
 size_t Tokenizer::ByteOffsetOfNthLine(const base::StringPiece& buf, int n) {
-  int cur_line = 1;
-  size_t cur_byte = 0;
-
-  DCHECK(n > 0);
+  DCHECK_GT(n, 0);
 
   if (n == 1)
     return 0;
 
+  int cur_line = 1;
+  size_t cur_byte = 0;
   while (cur_byte < buf.size()) {
     if (IsNewline(buf, cur_byte)) {
       cur_line++;
@@ -150,7 +149,7 @@
     }
     cur_byte++;
   }
-  return -1;
+  return static_cast<size_t>(-1);
 }
 
 // static