Add plumbing in blink to allow overriding the skia font manager.

content/child/font_warmup_win.cc

Index: content/child/font_warmup_win.cc
diff --git a/content/child/font_warmup_win.cc b/content/child/font_warmup_win.cc
index be532df2196d72111b7d2628ddbd310d81cc8fd6..076915588496c48182995c40bd8217f386cfe973 100644
--- a/content/child/font_warmup_win.cc
+++ b/content/child/font_warmup_win.cc
@@ -130,25 +130,6 @@ void CreateDirectWriteFactory(IDWriteFactory** factory) {
       reinterpret_cast<IUnknown**>(factory))));
 }
 
-HRESULT STDMETHODCALLTYPE StubFontCollection(IDWriteFactory* factory,
-                                             IDWriteFontCollection** col,
-                                             BOOL checkUpdates) {
-  // We always return pre-created font collection from here.
-  IDWriteFontCollection* custom_collection = GetCustomFontCollection(factory);
-  DCHECK(custom_collection != nullptr);
-  *col = custom_collection;
-  return S_OK;
-}
-
-void PatchDWriteFactory(IDWriteFactory* factory) {
-  const unsigned int kGetSystemFontCollectionVTableIndex = 3;
-
-  PROC* vtable = *reinterpret_cast<PROC**>(factory);
-  PROC* function_ptr = &vtable[kGetSystemFontCollectionVTableIndex];
-  void* stub_function = &StubFontCollection;
-  base::win::ModifyCode(function_ptr, &stub_function, sizeof(PROC));
-}
-
 // Class to fake out a DC or a Font object. Maintains a reference to a
 // SkTypeFace to emulate the simple operation of a DC and Font.
 class FakeGdiObject : public base::RefCountedThreadSafe<FakeGdiObject> {
@@ -478,12 +459,9 @@ SkFontMgr* GetPreSandboxWarmupFontMgr() {
     IDWriteFactory* factory;
     CreateDirectWriteFactory(&factory);
 
-    GetCustomFontCollection(factory);
-
-    PatchDWriteFactory(factory);
-
-    blink::WebFontRendering::setDirectWriteFactory(factory);
-    g_warmup_fontmgr = SkFontMgr_New_DirectWrite(factory);
+    g_warmup_fontmgr =
+        SkFontMgr_New_DirectWrite(factory, GetCustomFontCollection(factory));
+    blink::WebFontRendering::setSkiaFontManager(g_warmup_fontmgr);
   }
   return g_warmup_fontmgr;
 }