[Fuchsia] Lower the debug build binary size.

This changes the optimization level for debug builds on Fuchsia to
optimize for size. This fixes an issue where the KVM would run out of
space on the Fuchsia debug component bot.

Bug: 910243
Change-Id: I7b1257c26b820af97b7c29151cde8f1a52692f5e
Reviewed-on: https://chromium-review.googlesource.com/c/1352621
Commit-Queue: Fabrice de Gans-Riberi <fdegans@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612337}

build/config/compiler/BUILD.gn

@@ -1996,6 +1996,10 @@ config("no_optimize") {
     } else {
       cflags = [ "-Os" ] + common_optimize_on_cflags
     }
+  } else if (is_fuchsia) {
+    # On Fuchsia, we optimize for size here to reduce the size of debug build
+    # packages so they can be run in a KVM. See crbug.com/910243 for details.
+    cflags = [ "-Og" ]
   } else {
     cflags = [ "-O0" ]
     ldflags = []