remove mention of SkCanvas::kIsOpaque_SaveLayerFlag

I am preparing to remove this flag in Skia.  Beyond these two debug use
cases, the flag and the performance-only feature it enables appear to
only be used antagonistically by fuzzers.

Bug: skia:7566, chromium:808830
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I99c87f6600200e825aa7a1590d4031030d55af42
Reviewed-on: https://chromium-review.googlesource.com/905107Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534791}

skia/ext/benchmarking_canvas.cc

@@ -251,8 +251,6 @@ std::unique_ptr<base::Value> AsValue(const SkPaint& paint) {
 std::unique_ptr<base::Value> SaveLayerFlagsAsValue(
     SkCanvas::SaveLayerFlags flags) {
   FlagsBuilder builder('|');
-  builder.addFlag(flags & SkCanvas::kIsOpaque_SaveLayerFlag,
-                  "kIsOpaque");
   builder.addFlag(flags & SkCanvas::kPreserveLCDText_SaveLayerFlag,
                   "kPreserveLCDText");
 

third_party/WebKit/Source/platform/graphics/LoggingCanvas.cpp

@@ -512,8 +512,6 @@ String ClipOpName(SkClipOp op) {
 
 String SaveLayerFlagsToString(SkCanvas::SaveLayerFlags flags) {
   String flags_string = "";
-  if (flags & SkCanvas::kIsOpaque_SaveLayerFlag)
-    flags_string.append("kIsOpaque_SaveLayerFlag ");
   if (flags & SkCanvas::kPreserveLCDText_SaveLayerFlag)
     flags_string.append("kPreserveLCDText_SaveLayerFlag ");
   return flags_string;