Add comment about same-page navs to WCO::DidStart/FinishNavigation

content/public/browser/web_contents_observer.h

Index: content/public/browser/web_contents_observer.h
diff --git a/content/public/browser/web_contents_observer.h b/content/public/browser/web_contents_observer.h
index 32a11dd9be3a867304de28a005030d553062d000..5db620927adf80a521d2bf4ab737bfda6e779248 100644
--- a/content/public/browser/web_contents_observer.h
+++ b/content/public/browser/web_contents_observer.h
@@ -143,6 +143,10 @@ class CONTENT_EXPORT WebContentsObserver : public IPC::Listener,
   // Note that this is fired by navigations in any frame of the WebContents,
   // not just the main frame.
   //
+  // Note that this is fired by same-page navigations, such as fragment
+  // navigations or pushState/replaceState, which will not result in a document
+  // change. To filter these out, use NavigationHandle::IsSamePage.
+  //
   // Note that more than one navigation can be ongoing in the same frame at the
   // same time (including the main frame). Each will get its own
   // NavigationHandle.
@@ -178,6 +182,10 @@ class CONTENT_EXPORT WebContentsObserver : public IPC::Listener,
   // and related methods to listen for continued events from this
   // RenderFrameHost.
   //
+  // Note that this is fired by same-page navigations, such as fragment
+  // navigations or pushState/replaceState, which will not result in a document
+  // change. To filter these out, use NavigationHandle::IsSamePage.
+  //
   // Note that |navigation_handle| will be destroyed at the end of this call,
   // so do not keep a reference to it afterward.
   virtual void DidFinishNavigation(NavigationHandle* navigation_handle) {}