Rename local varaible name to font_cache_purge_preventer

This patch changes local variable name |fontCachePurgePreventer|[1] to
|font_cache_purge_preventer| to follow coding style.

This is follow-up of the CL[1].

[1] http://crrev.com/c/1969290: Prevent purging FontCache in
SetTextWithOffset

Bug: 982194
Change-Id: I31734397fea274d3665c7bdb15d03ea8a01c1574
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3225839
Commit-Queue: Yoshifumi Inoue <[email protected]>
Commit-Queue: Kent Tamura <[email protected]>
Auto-Submit: Yoshifumi Inoue <[email protected]>
Reviewed-by: Kent Tamura <[email protected]>
Cr-Commit-Position: refs/heads/main@{#931922}
NOKEYCHECK=True
GitOrigin-RevId: 08f15f837fa85bc4f33e1097769e932417c9c6a4

blink/renderer/core/layout/ng/inline/ng_inline_node.cc

@@ -914,7 +914,7 @@ bool NGInlineNode::SetTextWithOffset(LayoutText* layout_text,
 
   // This function runs outside of the layout phase. Prevent purging font cache
   // while shaping.
-  FontCachePurgePreventer fontCachePurgePreventer;
+  FontCachePurgePreventer font_cache_purge_preventer;
 
   String new_text(std::move(new_text_in));
   layout_text->StyleRef().ApplyTextTransform(&new_text,