Merge to XFA: Add ContainsKey() and ContainsValue() and use them where appropriate.

TBR=ochang@chromium.org

Review URL: https://codereview.chromium.org/1540263003 .

(cherry picked from commit 1fc92867ca53f0fba4272fbee3814d844f487495)

Review URL: https://codereview.chromium.org/1542193002 .
diff --git a/fpdfsdk/src/javascript/util.cpp b/fpdfsdk/src/javascript/util.cpp
index cb9c9b2..a14e81c 100644
--- a/fpdfsdk/src/javascript/util.cpp
+++ b/fpdfsdk/src/javascript/util.cpp
@@ -468,17 +468,13 @@
       case '\\':
         break;
       case '>': {
-        for (std::string::iterator it = cSource.begin(); it != cSource.end();
-             it++) {
-          *it = toupper(*it);
-        }
+        for (char& c : cSource)
+          c = toupper(c);
         break;
       }
       case '<': {
-        for (std::string::iterator it = cSource.begin(); it != cSource.end();
-             it++) {
-          *it = tolower(*it);
-        }
+        for (char& c : cSource)
+          c = tolower(c);
         break;
       }
       case '=':