Provide a way to disable libpci dependency.

Add a new gyp variable: use_libpci (default value is 1).
Add a new define when use_libpci==1: USE_LIBPCI.
Don't call specific PCI code in gpu_info_collector_linux.cc if USE_LIBPCI isn't defined.

BUG=427401
[email protected]

Review URL: https://codereview.chromium.org/692893004

Cr-Commit-Position: refs/heads/master@{#302613}
diff --git a/gpu/gpu_config.gypi b/gpu/gpu_config.gypi
index b90143f..4505503 100644
--- a/gpu/gpu_config.gypi
+++ b/gpu/gpu_config.gypi
@@ -65,7 +65,7 @@
         '../third_party/amd/amd_videocard_info_win.cc',
       ],
     }],
-    ['OS=="linux" and (use_x11==1 or use_ozone==1)', {
+    ['OS=="linux" and use_libpci==1 and (use_x11==1 or use_ozone==1)', {
       'dependencies': [
         '../build/linux/system.gyp:libpci',
       ],