[Autofill assistant] Fix |GetForWebContents|

|GetForWebContents| should only retrieve RuntimeManager for given web contents
and |GetOrCreateForWebContents| should create instance if one does not exist.

Bug: 1133783
Change-Id: Ib26162b69d1b3359fc571e139ba3724ec951aa12
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2453389Reviewed-by: Clemens Arbesser <arbesser@google.com>
Commit-Queue: Milica Selakovic <selakovic@google.com>
Cr-Commit-Position: refs/heads/master@{#814601}

components/autofill_assistant/browser/public/runtime_manager.cc

@@ -8,9 +8,14 @@
 namespace autofill_assistant {
 
 // static
-RuntimeManager* RuntimeManager::GetForWebContents(
+RuntimeManager* RuntimeManager::GetOrCreateForWebContents(
     content::WebContents* contents) {
   return RuntimeManagerImpl::GetForWebContents(contents);
 }
 
+RuntimeManager* RuntimeManager::GetForWebContents(
+    content::WebContents* contents) {
+  return RuntimeManagerImpl::FromWebContents(contents);
+}
+
 }  // namespace autofill_assistant

components/autofill_assistant/browser/public/runtime_manager.h

@@ -18,6 +18,11 @@ class RuntimeManager {
   // Returns the instance of RuntimeManager that was attached to the
   // specified WebContents. Creates a new instance if no instance was attached
   // to |contents| yet.
+  static RuntimeManager* GetOrCreateForWebContents(
+      content::WebContents* contents);
+
+  // Returns the instance of RuntimeManager that was attached to the
+  // specified WebContents. If no instance is attached method will return null.
   static RuntimeManager* GetForWebContents(content::WebContents* contents);
 
   // Add/Remove observers