Pass -Oz flag to Clang when targeting Android.

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 1c50195f048741211470d94b49c45a08202d0cee..64e82671449f64c3b6210de32c4334bc73e1a231 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -1441,7 +1441,11 @@ config("optimize") {
     # Favor size over speed.
     # TODO(crbug.com/718650): Fix -Os in PNaCl compiler and remove the is_nacl
     # guard above.
-    cflags = [ "-Os" ] + common_optimize_on_cflags
+    if (is_clang) {
+      cflags = [ "-Oz" ] + common_optimize_on_cflags
+    } else {
+      cflags = [ "-Os" ] + common_optimize_on_cflags
+    }
   } else {
     cflags = [ "-O2" ] + common_optimize_on_cflags
   }
@@ -1458,7 +1462,11 @@ config("optimize_no_wpo") {
     # Favor size over speed.
     # TODO(crbug.com/718650): Fix -Os in PNaCl compiler and remove the is_nacl
     # guard above.
-    cflags = [ "-Os" ] + common_optimize_on_cflags
+    if (is_clang) {
+      cflags = [ "-Oz" ] + common_optimize_on_cflags
+    } else {
+      cflags = [ "-Os" ] + common_optimize_on_cflags
+    }
   } else if (optimize_for_fuzzing) {
     cflags = [ "-O1" ] + common_optimize_on_cflags
   } else {
@@ -1478,7 +1486,11 @@ config("no_optimize") {
   } else if (is_android && !android_full_debug) {
     # On Android we kind of optimize some things that don't affect debugging
     # much even when optimization is disabled to get the binary size down.
-    cflags = [ "-Os" ]
+    if (is_clang) {
+      cflags = [ "-Oz" ] + common_optimize_on_cflags
+    } else {
+      cflags = [ "-Os" ] + common_optimize_on_cflags
+    }
   } else {
     cflags = [ "-O0" ]
     ldflags = []