Fix PDFium integration into other projects.

https://pdfium-review.googlesource.com/55931 accidentally added an
absolute reference in fxjs/BUILD.gn to //fpdfsdk/BUILD.gn. When
integrated into other projects, PDFium will be at a different location.
Fix this by switching to relative references.

TBR=tsepez@chromium.org

Change-Id: Ibbb9baa81aeb923a8eacd2b23051e15610fbc593
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/55970
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/fxjs/BUILD.gn b/fxjs/BUILD.gn
index 136c812..aad637a 100644
--- a/fxjs/BUILD.gn
+++ b/fxjs/BUILD.gn
@@ -243,7 +243,7 @@
     configs = [ "//v8:external_startup_data" ]
     deps = [
       ":fxjs",
-      "//fpdfsdk",
+      "../fpdfsdk",
     ]
     pdfium_root_dir = "../"