Add API to clear BlobCache when cache validation fails

SkSL shader cache requests a method to flush out entire BlobCache
when cache validation fails. Add a new API in BlobCache for the
action.

Bug: b/71800782
Test: hwui_unit_tests
Change-Id: Ife4db9a5d0523972133ec1a9744f001de050efeb
diff --git a/opengl/libs/EGL/BlobCache.h b/opengl/libs/EGL/BlobCache.h
index 1f5d535..e5c5e5b 100644
--- a/opengl/libs/EGL/BlobCache.h
+++ b/opengl/libs/EGL/BlobCache.h
@@ -97,6 +97,10 @@
     //
     int unflatten(void const* buffer, size_t size);
 
+    // clear flushes out all contents of the cache then the BlobCache, leaving
+    // it in an empty state.
+    void clear() { mCacheEntries.clear(); }
+
 protected:
     // mMaxTotalSize is the maximum size that all cache entries can occupy. This
     // includes space for both keys and values. When a call to BlobCache::set