If the user selects text in the current tab, and types CTRL-F,...

chrome/browser/renderer_host/render_view_host.h

Index: chrome/browser/renderer_host/render_view_host.h
===================================================================
--- chrome/browser/renderer_host/render_view_host.h	(revision 71618)
+++ chrome/browser/renderer_host/render_view_host.h	(working copy)
@@ -542,6 +542,9 @@
                         int renderer_id,
                         GURL* url);
 
+  // Gets the selected text in this view, or the empty string.
+  std::string selected_text();
+
  protected:
   // RenderWidgetHost protected overrides.
   virtual bool PreHandleKeyboardEvent(const NativeWebKeyboardEvent& event,
@@ -791,6 +794,9 @@
   // The termination status of the last render view that terminated.
   base::TerminationStatus render_view_termination_status_;
 
+  // The most recently selected text.
+  std::string selected_text_;
+
   DISALLOW_COPY_AND_ASSIGN(RenderViewHost);
 };