Purge hb font on Minikin font destruction

This patch eagerly purges the corresponding hb_font_t object from
the HbFontCache when the underlying MinikinFont is destroyed. After
that, the key will no longer be accessed, so having the entry is
wastes memory.

Bug: 27251075
Bug: 27860101
Change-Id: I1b98016133fe3baf6525ac37d970a65ddccadb4f

engine/src/flutter/include/minikin/MinikinFont.h

@@ -96,6 +96,8 @@ class MinikinFontFreeType;
 
 class MinikinFont : public MinikinRefCounted {
 public:
+    virtual ~MinikinFont();
+
     virtual float GetHorizontalAdvance(uint32_t glyph_id,
         const MinikinPaint &paint) const = 0;
 

engine/src/flutter/libs/minikin/Android.mk

@@ -32,6 +32,7 @@ minikin_src_files := \
     Measurement.cpp \
     MinikinInternal.cpp \
     MinikinRefCounted.cpp \
+    MinikinFont.cpp \
     MinikinFontFreeType.cpp \
     SparseBitSet.cpp \
     WordBreaker.cpp

engine/src/flutter/libs/minikin/HbFontCache.cpp

@@ -75,6 +75,10 @@ public:
         mCache.clear();
     }
 
+    void remove(int32_t fontId) {
+        mCache.remove(fontId);
+    }
+
 private:
     static const size_t kMaxEntries = 100;
 
@@ -95,6 +99,12 @@ void purgeHbFontCacheLocked() {
     getFontCacheLocked()->clear();
 }
 
+void purgeHbFont(const MinikinFont* minikinFont) {
+    AutoMutex _l(gMinikinLock);
+    const int32_t fontId = minikinFont->GetUniqueId();
+    getFontCacheLocked()->remove(fontId);
+}
+
 hb_font_t* getHbFontLocked(MinikinFont* minikinFont) {
     assertMinikinLocked();
     static hb_font_t* nullFaceFont = nullptr;

engine/src/flutter/libs/minikin/HbFontCache.h

@@ -23,6 +23,7 @@ namespace android {
 class MinikinFont;
 
 void purgeHbFontCacheLocked();
+void purgeHbFont(const MinikinFont* minikinFont);
 hb_font_t* getHbFontLocked(MinikinFont* minikinFont);
 
 }  // namespace android

engine/src/flutter/libs/minikin/MinikinFont.cpp

@@ -0,0 +1,26 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <minikin/MinikinFont.h>
+#include "HbFontCache.h"
+
+namespace android {
+
+MinikinFont::~MinikinFont() {
+    purgeHbFont(this);
+}
+
+}  // namespace android