Move TracedValue::ValueToString outside the class

Refactor function ValueToString from the class
base::trace_event::TracedValue into namespace base::trace_event.

This is a follow-up of http://crrev.com/c/2299722

Bug: 1103623
Change-Id: Ied92ce36da432d84fef4b186f902c8ac581b416b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2302029Reviewed-by: Oksana Zhuravlova <oksamyt@chromium.org>
Reviewed-by: Eric Seckler <eseckler@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Commit-Queue: Karel Král <karelkral@google.com>
Cr-Commit-Position: refs/heads/master@{#789379}

base/trace_event/traced_value.h

@@ -131,14 +131,6 @@ class BASE_EXPORT TracedValue : public ConvertableToTraceFormat {
     KeptValueType kept_value_type_;
   };
 
-  // Return std::string representation given by |value|'s ostream operator<<.
-  template <class T>
-  static std::string ValueToString(const T& value) {
-    std::stringstream ss;
-    ss << value;
-    return ss.str();
-  }
-
   // A custom serialization class can be supplied by implementing the
   // Writer interface and supplying a factory class to SetWriterFactoryCallback.
   // Primarily used by Perfetto to write TracedValues directly into its proto
@@ -239,6 +231,14 @@ class BASE_EXPORT TracedValueJSON : public TracedValue {
   std::string ToFormattedJSON() const;
 };
 
+// Return std::string representation given by |value|'s ostream operator<<.
+template <typename T>
+std::string ValueToString(const T& value) {
+  std::stringstream ss;
+  ss << value;
+  return ss.str();
+}
+
 }  // namespace trace_event
 }  // namespace base
 

base/trace_event/traced_value_unittest.cc

@@ -16,7 +16,7 @@ namespace base {
 namespace trace_event {
 
 TEST(TraceEventArgumentTest, ValueToString) {
-  std::string zero = TracedValue::ValueToString(0);
+  std::string zero = ValueToString(0);
   EXPECT_EQ("0", zero);
 }
 

mojo/public/tools/bindings/generators/mojom_cpp_generator.py

@@ -692,8 +692,8 @@ class Generator(generator.Generator):
       if self._IsTypemappedKind(kind) or IsNativeOnlyKind(kind):
         yield '%s->SetInteger("%s", static_cast<int>(%s));' % value_name_cppname
       else:
-        yield '%s->SetString("%s", base::trace_event::'\
-            'TracedValue::ValueToString(%s));' % value_name_cppname
+        yield '%s->SetString("%s", base::trace_event::ValueToString(%s));'\
+            % value_name_cppname
       return
     if mojom.IsStringKind(kind):
       if self.for_blink: