Prefix build variables used in separate repos with mojo_

mojo/public/mojo_application.gni

Index: mojo/public/mojo_application.gni
diff --git a/mojo/public/mojo_application.gni b/mojo/public/mojo_application.gni
index ce8cf9e12bf2756bd830dd353d65fff731d4b616..2c7ee4aec41a4b9ba0c59a6360aff115e7d01981 100644
--- a/mojo/public/mojo_application.gni
+++ b/mojo/public/mojo_application.gni
@@ -77,11 +77,11 @@ template("mojo_native_application") {
       }
 
       # Copy any necessary prebuilt artifacts.
-      if (use_prebuilt_mojo_shell) {
+      if (mojo_use_prebuilt_mojo_shell) {
         data_deps +=
             [ rebase_path("mojo/public/tools:copy_mojo_shell", ".", mojo_root) ]
       }
-      if (use_prebuilt_network_service) {
+      if (mojo_use_prebuilt_network_service) {
         data_deps += [ rebase_path("mojo/public/tools:copy_network_service",
                                    ".",
                                    mojo_root) ]
@@ -197,11 +197,11 @@ template("mojo_native_application") {
       }
 
       # Copy any necessary prebuilt artifacts.
-      if (use_prebuilt_mojo_shell) {
+      if (mojo_use_prebuilt_mojo_shell) {
         data_deps +=
             [ rebase_path("mojo/public/tools:copy_mojo_shell", ".", mojo_root) ]
       }
-      if (use_prebuilt_network_service) {
+      if (mojo_use_prebuilt_network_service) {
         data_deps += [ rebase_path("mojo/public/tools:copy_network_service",
                                    ".",
                                    mojo_root) ]