Enable FDO for v8 in android build.

build/toolchain.gypi

Index: build/toolchain.gypi
diff --git a/build/toolchain.gypi b/build/toolchain.gypi
index eddc32979fb4524ac6810afa04d071c6813d90ed..7f3b9e52d91dfab36ad3297e147d94f039664d0b 100644
--- a/build/toolchain.gypi
+++ b/build/toolchain.gypi
@@ -621,6 +621,12 @@
                 'cflags': [ '-m32' ],
                 'ldflags': [ '-m32' ],
               }],
+              # Enable feedback-directed optimisation when building in android.
+              [ 'android_webview_build == 1', {
+                'aosp_build_settings': {
+                  'LOCAL_FDO_SUPPORT': 'true',
+                },
+              }],
             ],
             'xcode_settings': {
               'ARCHS': [ 'i386' ],
@@ -645,6 +651,12 @@
                  'cflags': [ '-m64' ],
                  'ldflags': [ '-m64' ],
                }],
+               # Enable feedback-directed optimisation when building in android.
+               [ 'android_webview_build == 1', {
+                 'aosp_build_settings': {
+                   'LOCAL_FDO_SUPPORT': 'true',
+                 },
+               }],
              ]
            }],
          ],