GN: default to -O1

src/core/SkGlyphCache.cpp

Index: src/core/SkGlyphCache.cpp
diff --git a/src/core/SkGlyphCache.cpp b/src/core/SkGlyphCache.cpp
index 40d599717d0423031680f760b123c8f89ef100f4..a8eaa667a58ad72e4c5141fd34a1b4dcdcbae163 100644
--- a/src/core/SkGlyphCache.cpp
+++ b/src/core/SkGlyphCache.cpp
@@ -545,7 +545,7 @@ SkGlyphCache* SkGlyphCache::VisitCache(SkTypeface* typeface,
 
     // Precondition: the typeface id must be the fFontID in the descriptor
     SkDEBUGCODE(
-        uint32_t length;
+        uint32_t length = 0;
         const SkScalerContext::Rec* rec = static_cast<const SkScalerContext::Rec*>(
             desc->findEntry(kRec_SkDescriptorTag, &length));
         SkASSERT(rec);