Replace Handle<> with Local in remaining gin/*

Handle is an alias for Local

BUG=424445

Review URL: https://codereview.chromium.org/1112923003

Cr-Commit-Position: refs/heads/master@{#327672}
diff --git a/gin/function_template.cc b/gin/function_template.cc
index 7b85170..46285f9 100644
--- a/gin/function_template.cc
+++ b/gin/function_template.cc
@@ -18,7 +18,7 @@
   DCHECK(v8_ref_.IsEmpty());
 }
 
-v8::Handle<v8::External> CallbackHolderBase::GetHandle(v8::Isolate* isolate) {
+v8::Local<v8::External> CallbackHolderBase::GetHandle(v8::Isolate* isolate) {
   return v8::Local<v8::External>::New(isolate, v8_ref_);
 }