Fix path to pdfium_partition_alloc target.

The path should be relative, so it works correctly when PDFium is
embedded in another project. As is, the absolute path will look for
pdfium_partition_alloc in the top-level third_party directory. When
PDFium is embedded, that third_party directory belongs to the embedder.

Change-Id: I991e02b570eb3c2f88a7fb8d79c248c921de2de0
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/96770
Commit-Queue: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>

core/fxcrt/BUILD.gn

diff --git a/core/fxcrt/BUILD.gn b/core/fxcrt/BUILD.gn
index f17adc3..48bdc64 100644
--- a/core/fxcrt/BUILD.gn
+++ b/core/fxcrt/BUILD.gn
@@ -134,7 +134,7 @@
   ]
   if (!is_win || is_clang) {
     sources += [ "fx_memory_pa.cpp" ]
-    deps += [ "//third_party:pdfium_partition_alloc" ]
+    deps += [ "../../third_party:pdfium_partition_alloc" ]
   } else {
     sources += [ "fx_memory_malloc.cpp" ]
   }