Instrumented libraries: add a base.isolate entry for prebuilt libs.

base/base.isolate

Index: base/base.isolate
diff --git a/base/base.isolate b/base/base.isolate
index a2458194bf382c327436065e5a115f56f284cbc0..c7ba651ac71f0924cb9c0f25a66bc58a2aa89d0a 100644
--- a/base/base.isolate
+++ b/base/base.isolate
@@ -7,6 +7,8 @@
     # itself, virtually all targets using it has to include icu. The only
     # exception is the Windows sandbox (?).
     '../third_party/icu/icu.isolate',
+    # Sanitizer-instrumented third-party libraries (if enabled).
+    '../third_party/instrumented_libraries/instrumented_libraries.isolate',
   ],
   'conditions': [
     ['use_custom_libcxx==1', {
@@ -16,13 +18,6 @@
         ],
       },
     }],
-    ['use_instrumented_libraries==1', {
-      'variables': {
-        'files': [
-          '<(PRODUCT_DIR)/instrumented_libraries/',
-        ],
-      },
-    }],
     ['OS=="mac" and asan==1', {
       'variables': {
         'files': [