Move more string_util functions to base namespace.

Rename IsWhitespace to IsUnicodeWhitespace (to contrast it to the already-existing IsAsciiWhitespace).

De-inline HexDigitToInt. This is only used in a few places and I don't think it's necessary to inline.

Remove some redundant base:: qualifications in base.

TBR=sky

Review URL: https://codereview.chromium.org/1200053004

Cr-Commit-Position: refs/heads/master@{#335827}
diff --git a/sql/connection.cc b/sql/connection.cc
index b17457b3..d1b1049 100644
--- a/sql/connection.cc
+++ b/sql/connection.cc
@@ -812,7 +812,7 @@
     // sqlite3_exec() does this, presumably to avoid spinning the parser for
     // trailing whitespace.
     // TODO(shess): Audit to see if this can become a DCHECK.
-    while (IsAsciiWhitespace(*sql)) {
+    while (base::IsAsciiWhitespace(*sql)) {
       sql++;
     }