Fix TextDropShadowCache infinite loop

Bug: 26862239

Switch TextDropCacheShadow to use the tracked objectSize()
instead of the optional bitmapSize. A mismatch here
results in ::get() infinite looping trying to free space in
the cache since the LRU removal callback would always
decrement mSize by 0 since bitmapSize was not being set.

Also prevent the infinite loop in the future by crashing if
this scenario happens again.

Change-Id: Ib4e9fbe1c8327af2335ad650fd694a1627d9824f
diff --git a/libs/hwui/Android.mk b/libs/hwui/Android.mk
index fc40554..587a366 100644
--- a/libs/hwui/Android.mk
+++ b/libs/hwui/Android.mk
@@ -248,7 +248,8 @@
     tests/unit/VectorDrawableTests.cpp \
     tests/unit/OffscreenBufferPoolTests.cpp \
     tests/unit/StringUtilsTests.cpp \
-    tests/unit/BufferPoolTests.cpp
+    tests/unit/BufferPoolTests.cpp \
+    tests/unit/TextDropShadowCacheTests.cpp
 
 ifeq (true, $(HWUI_NEW_OPS))
     LOCAL_SRC_FILES += \