Use default optimization on Android for zlib inflate chunk copy

Speculative fix: back off from using -O3 on Android for the inflate
chunk copy code to see if -O3 caused the perf bot regression on the
Android One bot, http://bit.ly/2AfaxhG

Bug: 772870
Change-Id: I06bd941224dacbc5d7024a65934faaa53e4a4ce5
Reviewed-on: https://chromium-review.googlesource.com/823503
Commit-Queue: Noel Gordon <noel@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>
Reviewed-by: Chris Blume <cblume@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523679}

third_party/zlib/BUILD.gn

@@ -94,11 +94,13 @@ source_set("zlib_inflate_chunk_simd") {
         "contrib/optimizations/inflate.c",
       ]
 
-      if (!is_debug) {
-        # Use optimize_speed (-O3) to output the _smallest_ code.
-        configs -= [ "//build/config/compiler:default_optimization" ]
-        configs += [ "//build/config/compiler:optimize_speed" ]
-      }
+      # TODO(772870) back off from -O3 while investigating Android
+      # One perf bot PNG decode regression.
+      # if (!is_debug) {
+      #  # Use optimize_speed (-O3) to output the _smallest_ code.
+      #  configs -= [ "//build/config/compiler:default_optimization" ]
+      #  configs += [ "//build/config/compiler:optimize_speed" ]
+      # }
     }
   }