Reland https://skia-review.googlesource.com/c/6091/

The only difference is that we now also put the guard flag
SK_SUPPORT_LEGACY_AAA in SkUserConfig.h. Previously, SkAnalyticEdge.cpp doesn't
get that flag from SkScan.h and that caused many problems.

BUG=skia:
TBR=reed@google.com,caryclark@google.com

Change-Id: I134bb76cebd6fffa712f438076668765321bba3b
Reviewed-on: https://skia-review.googlesource.com/6992
Reviewed-by: Yuqian Li <liyuqian@google.com>
Commit-Queue: Yuqian Li <liyuqian@google.com>
diff --git a/dm/DM.cpp b/dm/DM.cpp
index 7774d5e..26883b1 100644
--- a/dm/DM.cpp
+++ b/dm/DM.cpp
@@ -1289,6 +1289,10 @@
 
     gSkUseAnalyticAA = FLAGS_analyticAA;
 
+    if (FLAGS_forceAnalyticAA) {
+        gSkForceAnalyticAA = true;
+    }
+
     if (FLAGS_verbose) {
         gVLog = stderr;
     } else if (!FLAGS_writePath.isEmpty()) {