[Skia] Add SK_SUPPORT_LEGACY_BLOB_BOUNDS config option.

To suppress upcoming changes in text blob bounds calculation.

BUG=451401
R=reed@google.com

Review URL: https://codereview.chromium.org/881323002

Cr-Commit-Position: refs/heads/master@{#313533}

skia/config/SkUserConfig.h

@@ -270,6 +270,10 @@ SK_API void SkDebugf_FileLine(const char* file, int line, bool fatal,
 #    define SK_DYNAMIC_ANNOTATIONS_ENABLED 1
 #endif
 
+#ifndef SK_SUPPORT_LEGACY_BLOB_BOUNDS
+#   define SK_SUPPORT_LEGACY_BLOB_BOUNDS
+#endif
+
 // ===== End Chrome-specific definitions =====
 
 #endif