Quote flags in GN.

Previously cflags/ldflags/etc. were not automatically quoted by GN. The
original intention was to support having multiple flags in one string which we
don in GYP in some cases (e.g. "-foo -bar"). But this ends up not being
necessary and we never do it.

Furthermore, GN still escapes quote characters in these flags, making it
impossible to manually quote them. The result is the old policy actively
prevents using spaces or quotes in flags. This change automatically quotes
flags like defines and file names already were.

Review URL: https://codereview.chromium.org/1879723002

Cr-Original-Commit-Position: refs/heads/master@{#386490}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: d923cf82900e3c26ab4f989cff62bf2bd6c2810f

tools/gn/ninja_binary_target_writer.cc

diff --git a/tools/gn/ninja_binary_target_writer.cc b/tools/gn/ninja_binary_target_writer.cc
index eaae098..7077b17 100644
--- a/tools/gn/ninja_binary_target_writer.cc
+++ b/tools/gn/ninja_binary_target_writer.cc
@@ -51,12 +51,6 @@
 EscapeOptions GetFlagOptions() {
   EscapeOptions opts;
   opts.mode = ESCAPE_NINJA_COMMAND;
-
-  // Some flag strings are actually multiple flags that expect to be just
-  // added to the command line. We assume that quoting is done by the
-  // buildfiles if it wants such things quoted.
-  opts.inhibit_quoting = true;
-
   return opts;
 }