Fix crash when attempting to use a font fallback chain with a custom font.

src/ports/SkFontConfigInterface_android.cpp

 
 /*
  * Copyright 2013 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkFontConfigInterface.h"
 #include "SkTypeface_android.h"
@@ skipping 551 matching lines @@
                                                               SkFontID origFontID,
                                                               const SkPaintOptionsAndroid& opts) {
     // Skia does not support font fallback by default. This enables clients such
     // as WebKit to customize their font selection. In any case, clients can use
     // GetFallbackFamilyNameForChar() to get the fallback font for individual
     // characters.
     if (!opts.isUsingFontFallbacks()) {
         return NULL;
     }
 
-    const SkTypeface* currTypeface = SkTypefaceCache::FindByID(currFontID);
-    SkASSERT(currTypeface != 0);
-
     FallbackFontList* currentFallbackList = findFallbackFontList(opts.getLanguage());
     SkASSERT(currentFallbackList);
 
     // we must convert currTypeface into a FontRecID
-    FontRecID currFontRecID = ((FontConfigTypeface*)currTypeface)->getIdentity().fID;
-    SkASSERT(INVALID_FONT_REC_ID != currFontRecID);
+    FontRecID currFontRecID = INVALID_FONT_REC_ID;
+    const SkTypeface* currTypeface = SkTypefaceCache::FindByID(currFontID);
+    // non-system fonts are not in the font cache so if we are asked to fallback
+    // for a non-system font we will start at the front of the chain.
+    if (NULL != currTypeface && currFontID == origFontID) {
+        currFontRecID = ((FontConfigTypeface*)currTypeface)->getIdentity().fID;
+        SkASSERT(INVALID_FONT_REC_ID != currFontRecID);
+    }
 
-    // TODO lookup the index next font in the chain
+    // lookup the index next font in the chain
     int currFallbackFontIndex = currentFallbackList->find(currFontRecID);
+    // We add 1 to the returned index for 2 reasons: (1) if find succeeds it moves
+    // our index to the next entry in the list; (2) if find() fails it returns
+    // -1 and incrementing it will set our starting index to 0 (the head of the list)
     int nextFallbackFontIndex = currFallbackFontIndex + 1;
 
     if(nextFallbackFontIndex >= currentFallbackList->count()) {
         return NULL;
     }
 
     // If a rec object is set to prefer "kDefault_Variant" it means they have no preference
     // In this case, we set the value to "kCompact_Variant"
     SkPaintOptionsAndroid::FontVariant variant = opts.getFontVariant();
     if (variant == SkPaintOptionsAndroid::kDefault_Variant) {
@@ skipping 195 matching lines @@
     return SkCreateTypefaceForScriptNG(getHBScriptFromHBScriptOld(script), style, fontVariant);
 }
 
 #endif
 
 ///////////////////////////////////////////////////////////////////////////////
 
 SkFontMgr* SkFontMgr::Factory() {
     return NULL;
 }