Turn on PGO for Skia on Android

This patch is to turn on PGO for skia on Android, which will provide a
performance improvement of 7.6% for hwui when applied PGO for both.

The patch specified a skia.profdata file, which locates in internal
google_data/pgo_profile directory, to work as the profile to feed PGO.
This profdata can be re-collected with PGO build system support.

PGO can be turned off by setting ANDROID_PGO_NO_PROFILE_USE environment
variable or set variable to false.

Test: Build skia successfully and verified the performance improvement
on device through benchmark.

BUG=skia:

Change-Id: I826f417569b2853630f6d4fcce236b5bc36547fa
Reviewed-on: https://skia-review.googlesource.com/82880
Commit-Queue: Derek Sollenberger <djsollen@google.com>
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Reviewed-by: John Reck <jreck@google.com>

gn/gn_to_bp.py

@@ -91,7 +91,24 @@ cc_library_static {
         },
     },
 
-    defaults: ["skia_deps"],
+    defaults: ["skia_deps",
+               "skia_pgo",
+    ],
+}
+
+// Build libskia with PGO by default.
+// Location of PGO profile data is defined in build/soong/cc/pgo.go
+// and is separate from skia.
+// To turn it off, set ANDROID_PGO_NO_PROFILE_USE environment variable
+// or set enable_profile_use property to false.
+cc_defaults {
+    name: "skia_pgo",
+    pgo: {
+        instrumentation: true,
+        profile_file: "skia/skia.profdata",
+        benchmarks: ["hwui", "skia"],
+        enable_profile_use: true,
+    },
 }
 
 cc_defaults {