Fix fallthrough warning

Fix a single fallthrough warning and re-enable -Wimplicit-fallthrough.

Test: m libhwui
Change-Id: I850f53f717417f70c9d0416176d03fd64473d1ba

libs/hwui/Android.bp

@@ -234,9 +234,6 @@ cc_defaults {
         "protos/graphicsstats.proto",
     ],
 
-    // Allow implicit fallthroughs in HardwareBitmapUploader.cpp until they are fixed.
-    cflags: ["-Wno-implicit-fallthrough"],
-
     proto: {
         export_proto_headers: true,
     },

libs/hwui/HardwareBitmapUploader.cpp

@@ -302,6 +302,7 @@ static FormatInfo determineFormat(const SkBitmap& skBitmap, bool usingGL) {
     switch (skBitmap.info().colorType()) {
         case kRGBA_8888_SkColorType:
             formatInfo.isSupported = true;
+            [[fallthrough]];
         // ARGB_4444 is upconverted to RGBA_8888
         case kARGB_4444_SkColorType:
             formatInfo.pixelFormat = PIXEL_FORMAT_RGBA_8888;