Linux: move hardcoded paths to GYP variables.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 4cd33e14db491f861b0033dee00263c41bb792de..c19713b2d8f5103517dc91237a383f74e42c72f1 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -90,7 +90,18 @@
     #
     # Developers should read
     #  http://code.google.com/p/chromium/wiki/LinuxSUIDSandboxDevelopment
-    'linux_suid_sandbox_restrictions': 'Path',
+    'linux_suid_sandbox_restrictions%': 'Path',
+
+    # This is the location of the sandbox binary. Chrome looks for this before
+    # running the zygote process. If found, and SUID, it will be used to
+    # sandbox the zygote process and, thus, all renderer processes.
+    'linux_sandbox_path%': '',
+
+    # If |linux_suid_sandbox_restrictions|, above, is 'Path' then only a single
+    # path is allowed to be exec'ed by the sandbox for security reasons. That
+    # path is set here. It should be the final location of the Chromium binary
+    # on the system.
+    'linux_sandbox_chrome_path%': '/opt/google/chrome/chrome',
   },
   'target_defaults': {
     'conditions': [