Rename GetMainFrame to GetPrimaryMainFrame

Progressively rename some usages of GetMainFrame to GetPrimaryMainFrame.

This is an automated change via emacs xref integration via codesearch.

BUG=1250404

Change-Id: Ibb5ca2055776693b332e26d7b348b81d65d1900c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3692390
Owners-Override: Nasko Oskov <[email protected]>
Commit-Queue: Dave Tapuska <[email protected]>
Reviewed-by: Nasko Oskov <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1011655}
diff --git a/components/find_in_page/find_tab_helper.cc b/components/find_in_page/find_tab_helper.cc
index 4aa33ba..a1d8477 100644
--- a/components/find_in_page/find_tab_helper.cc
+++ b/components/find_in_page/find_tab_helper.cc
@@ -127,8 +127,9 @@
 }
 
 void FindTabHelper::ActivateFindInPageResultForAccessibility() {
-  GetWebContents().GetMainFrame()->ActivateFindInPageResultForAccessibility(
-      current_find_request_id_);
+  GetWebContents()
+      .GetPrimaryMainFrame()
+      ->ActivateFindInPageResultForAccessibility(current_find_request_id_);
 }
 
 std::u16string FindTabHelper::GetInitialSearchText() {