ccpr: Fix an overzealous assert in DDL

Bug: skia:
Change-Id: I307e826704ad28d8ef4810b321258d4ac57929a1
Reviewed-on: https://skia-review.googlesource.com/c/164718
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
diff --git a/src/gpu/ccpr/GrCCPathCache.h b/src/gpu/ccpr/GrCCPathCache.h
index 8265ea5..742e7b1 100644
--- a/src/gpu/ccpr/GrCCPathCache.h
+++ b/src/gpu/ccpr/GrCCPathCache.h
@@ -97,7 +97,7 @@
     SkTInternalLList<GrCCPathCacheEntry> fLRU;
     SkMessageBus<sk_sp<GrCCPathCacheEntry>>::Inbox fInvalidatedEntriesInbox;
 
-    SkDEBUGCODE(SkThreadID fGraphicsThreadID);
+    SkDEBUGCODE(SkThreadID fGraphicsThreadID = kIllegalThreadID);
 };
 
 /**