Fix minikin_unittests

This CL fixes following test cases in minikin_tests
- FontFamilyTest.hasVariationSelectorTest
- HbFontCacheTest.getHbFontLockedTest
- HbFontCacheTest.purgeCacheTest

For the fix of FontFamilyTest.hasVariationSelectorTest, removing virtual
from GetUniqueId() in MinikinFont.  After [1], MinikinFont's destructor
started calling purgeHbCache() which calls virtual method,
MinikinFont::GetUniqueId().  Fortunately, the SkTypeface::uniqueID()
returns just internal value, so we can store it at the construction time
and use it instead of calling SkTypeface::uniqueID() every time.

This patch also changes purgeHbFont to purgeHbFontLocked, as all uses of
it were already under global mutex. This change avoids deadlock on
explicit unref, as when invoked by a Java finalizer from the Java object
that holds a reference to the font.

Some of the tests needed to change to using the ref counting protocol
rather than explicitly destructing font objects, as well.

[1] 9afcc6e2bd4d89e4e1deb6e18c3c4daca4e114fd

Bug: 28105730
Bug: 28105688
Change-Id: Ie5983c4869147dacabdca81af1605066cd680b3f

3 files changed, 23 insertions, 5 deletions

diff --git a/include/minikin/MinikinFont.h b/include/minikin/MinikinFont.h
index 0298235..4951514 100644
--- a/include/minikin/MinikinFont.h
+++ b/include/minikin/MinikinFont.h
@@ -99,6 +99,8 @@ typedef void (*MinikinDestroyFunc) (void* data);
 
 class MinikinFont : public MinikinRefCounted {
 public:
+    MinikinFont(int32_t uniqueId) : mUniqueId(uniqueId) {}
+
     virtual ~MinikinFont();
 
     virtual float GetHorizontalAdvance(uint32_t glyph_id,
@@ -125,12 +127,14 @@ public:
         return 0;
     }
 
-    virtual int32_t GetUniqueId() const = 0;
-
     static uint32_t MakeTag(char c1, char c2, char c3, char c4) {
         return ((uint32_t)c1 << 24) | ((uint32_t)c2 << 16) |
             ((uint32_t)c3 << 8) | (uint32_t)c4;
     }
+
+    int32_t GetUniqueId() const { return mUniqueId; }
+private:
+    const int32_t mUniqueId;
 };
 
 }  // namespace android
diff --git a/include/minikin/MinikinFontFreeType.h b/include/minikin/MinikinFontFreeType.h
index 535c249..baa08df 100644
--- a/include/minikin/MinikinFontFreeType.h
+++ b/include/minikin/MinikinFontFreeType.h
@@ -52,8 +52,6 @@ public:
 
     // TODO: provide access to raw data, as an optimization.
 
-    int32_t GetUniqueId() const;
-
     // Not a virtual method, as the protocol to access rendered
     // glyph bitmaps is probably different depending on the
     // backend.
@@ -64,7 +62,6 @@ public:
 
 private:
     FT_Face mTypeface;
-    int32_t mUniqueId;
     static int32_t sIdCounter;
 };
 
diff --git a/include/minikin/MinikinRefCounted.h b/include/minikin/MinikinRefCounted.h
index 74d27fe..603aff0 100644
--- a/include/minikin/MinikinRefCounted.h
+++ b/include/minikin/MinikinRefCounted.h
@@ -37,6 +37,23 @@ private:
     int mRefcount_;
 };
 
+// An RAII container for reference counted objects.
+// Note: this is only suitable for clients which are _not_ holding the global lock.
+template <typename T>
+class MinikinAutoUnref {
+public:
+    MinikinAutoUnref(T* obj) : mObj(obj) {
+    }
+    ~MinikinAutoUnref() {
+        mObj->Unref();
+    }
+    T& operator*() const { return *mObj; }
+    T* operator->() const { return mObj; }
+    T* get() const { return mObj; }
+private:
+    T* mObj;
+};
+
 }
 
 #endif   // MINIKIN_REF_COUNTED_H
\ No newline at end of file