Enable compiler optimizations on Harfbuzz

Experiments with hb-shape show that enabling compiler optimizations
improves performance of text shaping (therefore should help layout).

Initial tests show an improvement of 10.4% in hindi-line-layout
and 12.1% in latin-ebook performance layout tests.

Binary-Size: compiler optimized library will increase the size of the apk.
Bug: 902782
Change-Id: Iee50a04403ec634efec17be5ef8a72b996711a2f
Reviewed-on: https://chromium-review.googlesource.com/c/1321250
Commit-Queue: Adenilson Cavalcanti <cavalcantii@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Reviewed-by: Behdad Esfahbod <behdad@chromium.org>
Reviewed-by: Dominik Röttsches <drott@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606240}

third_party/harfbuzz-ng/BUILD.gn

@@ -205,6 +205,13 @@ if (use_system_harfbuzz) {
       # correctly.
       ":harfbuzz_warnings",
     ]
+
+    # This allows the compiler to do further optimizations in the code.
+    if (!is_debug) {
+      configs -= [ "//build/config/compiler:default_optimization" ]
+      configs += [ "//build/config/compiler:optimize_speed" ]
+    }
+
     public_configs = [ ":harfbuzz_config" ]
 
     deps = [