Allow non-component debug builds on iOS.

iOS does not support component build so we need to add an exception for
this platform. Bots did not fail because they compile with
symbol_level=1.

Bug: 945515
Change-Id: Idae7de4933f4ad4647a0598074145173e8e001c9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1541784
Auto-Submit: Olivier Robin <olivierrobin@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Commit-Queue: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#645266}

build/config/compiler/compiler.gni

@@ -258,8 +258,9 @@ if (symbol_level == -1) {
 # combination. This is only checked when current_toolchain == default_toolchain
 # because the is_component_build flag is set to false in various components of
 # the build (like nacl) and we don't want to assert on those.
+# iOS does not support component builds so add an exception for this platform.
 assert(symbol_level != 2 || current_toolchain != default_toolchain ||
-           is_component_build || !is_debug,
+           is_component_build || !is_debug || is_ios,
        "Can't do non-component debug builds at symbol_level=2")
 
 # Assert that the configuration isn't going to hit https://crbug.com/648948.