Add an analysis option to disable cache flushing.

pkg/analyzer/lib/src/context/cache.dart

Index: pkg/analyzer/lib/src/context/cache.dart
diff --git a/pkg/analyzer/lib/src/context/cache.dart b/pkg/analyzer/lib/src/context/cache.dart
index bf981e5fa0e1e2a2fce1b48c140ba8a6e1a2c318..ef780314a2ee2c4f4decd1415f00ebc3fb6e83c3 100644
--- a/pkg/analyzer/lib/src/context/cache.dart
+++ b/pkg/analyzer/lib/src/context/cache.dart
@@ -1229,7 +1229,8 @@ abstract class CachePartition {
    */
   CacheFlushManager _getFlushManager(ResultDescriptor descriptor) {
     ResultCachingPolicy policy = descriptor.cachingPolicy;
-    if (identical(policy, DEFAULT_CACHING_POLICY)) {
+    if (identical(policy, DEFAULT_CACHING_POLICY) ||
+        context.analysisOptions.disableCacheFlushing) {
       return UnlimitedCacheFlushManager.INSTANCE;
     }
     CacheFlushManager manager = _flushManagerMap[policy];