Add option to specify font fallback when creating the skia font manager

src/ports/SkFontMgr_win_dw.cpp

Index: src/ports/SkFontMgr_win_dw.cpp
diff --git a/src/ports/SkFontMgr_win_dw.cpp b/src/ports/SkFontMgr_win_dw.cpp
index 11afec3b53623205dad6612ab7cc0057c958181e..6b1004a009925f5feef0b0a46f4654cbe37cdab5 100644
--- a/src/ports/SkFontMgr_win_dw.cpp
+++ b/src/ports/SkFontMgr_win_dw.cpp
@@ -264,8 +264,11 @@ class SkFontMgr_DirectWrite : public SkFontMgr {
 public:
     /** localeNameLength must include the null terminator. */
     SkFontMgr_DirectWrite(IDWriteFactory* factory, IDWriteFontCollection* fontCollection,
-                          WCHAR* localeName, int localeNameLength)
+                          IDWriteFontFallback* fallback, WCHAR* localeName, int localeNameLength)
         : fFactory(SkRefComPtr(factory))
+#if SK_HAS_DWRITE_2_H
+        , fFontFallback(SkSafeRefComPtr(fallback))
+#endif
         , fFontCollection(SkRefComPtr(fontCollection))
         , fLocaleName(localeNameLength)
     {
@@ -275,6 +278,9 @@ public:
             // http://blogs.msdn.com/b/oldnewthing/archive/2004/03/26/96777.aspx
             SkASSERT_RELEASE(nullptr == fFactory2.get());
         }
+        if (fFontFallback.get()) {
+          SkASSERT(fFactory2.get());

[bungeman-skia, 2016/04/14 21:48:39]

nit: Skia uses 4 space indents.

[Ilya Kulshin, 2016/04/14 22:30:37]

Done.

+        }
 #endif
         memcpy(fLocaleName.get(), localeName, localeNameLength * sizeof(WCHAR));
     }
@@ -309,6 +315,7 @@ private:
     SkTScopedComPtr<IDWriteFactory> fFactory;
 #if SK_HAS_DWRITE_2_H
     SkTScopedComPtr<IDWriteFactory2> fFactory2;
+    SkTScopedComPtr<IDWriteFontFallback> fFontFallback;
 #endif
     SkTScopedComPtr<IDWriteFontCollection> fFontCollection;
     SkSMallocWCHAR fLocaleName;
@@ -763,8 +770,13 @@ SkTypeface* SkFontMgr_DirectWrite::onMatchFamilyStyleCharacter(const char family
 
 #if SK_HAS_DWRITE_2_H
     if (fFactory2.get()) {
-        SkTScopedComPtr<IDWriteFontFallback> fontFallback;
-        HRNM(fFactory2->GetSystemFontFallback(&fontFallback), "Could not get system fallback.");
+        SkTScopedComPtr<IDWriteFontFallback> systemFontFallback;
+        IDWriteFontFallback* fontFallback = fFontFallback.get();
+        if (!fontFallback) {
+            HRNM(fFactory2->GetSystemFontFallback(&systemFontFallback),
+                 "Could not get system fallback.");
+            fontFallback = systemFontFallback.get();
+        }

[bungeman-skia, 2016/04/14 21:48:39]

Hmmm... I see. The idea is that while making the transition we aren't using this
anyway, so get the default here if needed. If we tried to get the default in
SkFontMgr_New_DirectWrite then we'd end up trying to get one, which we don't
want.

So after Chromium provides an IDWriteFontFallback to SkFontMgr_New_DirectWrite,
this default code could be moved out to the constructor (since Chromium would no
longer be going down the path which would create the default).

[Ilya Kulshin, 2016/04/14 22:30:37]

Yes, after Chromium starts providing the fallback, Chromium wouldn't end up in
this block. However I'm not sure about other users of Skia. We've seen in
Chromium that creating the fallback is potentially expensive, so I'm somewhat
reluctant to create it automatically in the constructor if it might not even be
needed.

 
         SkTScopedComPtr<IDWriteNumberSubstitution> numberSubstitution;
         HRNM(fFactory2->CreateNumberSubstitution(DWRITE_NUMBER_SUBSTITUTION_METHOD_NONE, nullptr, TRUE,
@@ -1069,6 +1081,12 @@ SkTypeface* SkFontStyleSet_DirectWrite::matchStyle(const SkFontStyle& pattern) {
 
 SK_API SkFontMgr* SkFontMgr_New_DirectWrite(IDWriteFactory* factory,
                                             IDWriteFontCollection* collection) {
+    return SkFontMgr_New_DirectWrite(factory, collection, nullptr);
+}
+
+SK_API SkFontMgr* SkFontMgr_New_DirectWrite(IDWriteFactory* factory,
+                                            IDWriteFontCollection* collection,
+                                            IDWriteFontFallback* fallback) {
     if (nullptr == factory) {
         factory = sk_get_dwrite_factory();
         if (nullptr == factory) {
@@ -1099,7 +1117,7 @@ SK_API SkFontMgr* SkFontMgr_New_DirectWrite(IDWriteFactory* factory,
         };
     }
 
-    return new SkFontMgr_DirectWrite(factory, collection, localeName, localeNameLen);
+    return new SkFontMgr_DirectWrite(factory, collection, fallback, localeName, localeNameLen);
 }
 
 #include "SkFontMgr_indirect.h"