Move DevTools out of ash and turn it to a component.

components/ui_devtools/string_util.h

Index: components/ui_devtools/string_util.h
diff --git a/components/ui_devtools/string_util.h b/components/ui_devtools/string_util.h
index d08b8b6f22f68474b50ba3115e63e129d4e8e7bc..7e9f2957d487dc6971124c1ccd7c3cf180a82d50 100644
--- a/components/ui_devtools/string_util.h
+++ b/components/ui_devtools/string_util.h
@@ -28,9 +28,7 @@ class CustomStringBuilder {
   void reserveCapacity(std::size_t size) { s_.reserve(size); }
   void append(const String& s) { s_ += s; }
   void append(char c) { s_ += c; }
-  void append(const char* data, unsigned int length) {
-    s_.append(data, length);
-  }
+  void append(const char* data, size_t length) { s_.append(data, length); }
   String toString() { return s_; }
 };