Use font linking based on the original run font in RenderTextWin.

ui/gfx/render_text_win.cc

Index: ui/gfx/render_text_win.cc
===================================================================
--- ui/gfx/render_text_win.cc	(revision 133499)
+++ ui/gfx/render_text_win.cc	(working copy)
@@ -597,6 +597,7 @@
     bool tried_fallback = false;
     size_t linked_font_index = 0;
     const std::vector<Font>* linked_fonts = NULL;
+    Font original_font = run->font;
 
     // Select the font desired for glyph generation.
     SelectObject(cached_hdc_, run->font.GetNativeFont());
@@ -661,9 +662,17 @@
 
       // The meta file approach did not yield a replacement font, try to find
       // one using font linking. First time through, get the linked fonts list.
-      if (linked_fonts == NULL)
-        linked_fonts = GetLinkedFonts(run->font);
+      if (linked_fonts == NULL) {
+        // First, try to get the list for the original font.
+        linked_fonts = GetLinkedFonts(original_font);
 
+        // If there are no linked fonts for the original font, try querying the
+        // ones for the Uniscribe fallback font. This may happen if the first
+        // font is a custom font that has no linked fonts in the Registry.

[msw, 2012/04/23 20:20:59]

nit: Should registry be capitalized? Are you referring to the Windows Registry?

[Alexei Svitkine (slow), 2012/04/23 21:13:14]

Yes, the Windows Registry. It's capitalized in the comment for
QueryLinkedFontsFromRegistry(), so I've kept it consistent...

+        if (linked_fonts->empty())
+          linked_fonts = GetLinkedFonts(run->font);

[msw, 2012/04/23 20:20:59]

Have you considered appending the linked fonts for the Uniscribe fallback to the
list gathered for |original_font|, regardless of those available for the
original font? (more font options = better)?

[Alexei Svitkine (slow), 2012/04/23 21:13:14]

I've thought about it, but decided to keep it up my sleeve for now until/if
there's evidence that it would actually help things. Here's my reasoning:

First, it's clear that there's a benefit to the approach I'm taking here (when
the first list is empty) since it makes fallback work with a custom font.

But I can't really think of a scenario where it would help merging the lists
when the first one is not empty already (other than users munging around in
their Registry font linking settings, which is unsupported).

On the other hand, if the system truly doesn't have fonts to render something,
then traversing two link chains may just hurt performance without helping
anything.

So I'd rather keep that idea up my sleeve until/if there's a real scenario that
may benefit from it.

[msw, 2012/04/24 00:05:11]

Cool, how about a TODO or less directed/actionable comment mentioning that
possibility for future investigations?

+      }
+
       // None of the linked fonts worked, break out of the loop.
       if (linked_font_index == linked_fonts->size()) {
         // TODO(msw): Don't use SCRIPT_UNDEFINED. Apparently Uniscribe can