Tag some of Mojo heap allocations for the heap profiler.

ios/web/webui/mojo_facade.mm

Index: ios/web/webui/mojo_facade.mm
diff --git a/ios/web/webui/mojo_facade.mm b/ios/web/webui/mojo_facade.mm
index bc9b59e031c2fcde9e4a435161377f1c902ad5d8..6b02efb288c5bff1b02cb4f965b7ffdaddbdadc0 100644
--- a/ios/web/webui/mojo_facade.mm
+++ b/ios/web/webui/mojo_facade.mm
@@ -4,12 +4,15 @@
 
 #import "ios/web/webui/mojo_facade.h"
 
+#include <utility>
+
 #import <Foundation/Foundation.h>
 
 #import "base/ios/block_types.h"
 #include "base/json/json_reader.h"
 #include "base/json/json_writer.h"
 #import "base/mac/bind_objc_block.h"
+#include "base/memory/ptr_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/values.h"
 #import "ios/web/public/web_state/js/crw_js_injection_evaluator.h"
@@ -256,9 +259,9 @@ std::unique_ptr<base::Value> MojoFacade::HandleSupportWatch(
                                    callback_id, result];
     [script_evaluator_ executeJavaScript:script completionHandler:nil];
   });
-
-  mojo::Watcher& watcher = watchers_[++last_watch_id_];
-  watcher.Start(static_cast<mojo::Handle>(handle), signals, callback);
+  mojo::Watcher* watcher = new mojo::Watcher(FROM_HERE);
+  watchers_.insert(std::make_pair(++last_watch_id_, base::WrapUnique(watcher)));
+  watcher->Start(static_cast<mojo::Handle>(handle), signals, callback);
   return ValueFromInteger(last_watch_id_);
 }