Move enable_pdf to a buildflag header.

pdf/BUILD.gn

Index: pdf/BUILD.gn
diff --git a/pdf/BUILD.gn b/pdf/BUILD.gn
index 4e4d94655484680ba9b56b98c959e4fd31fc66d2..8afa86c07d5f7cea3b23967ffd8849c9a329f1f4 100644
--- a/pdf/BUILD.gn
+++ b/pdf/BUILD.gn
@@ -2,86 +2,99 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build/buildflag_header.gni")
 import("//build/config/features.gni")
+import("//pdf/features.gni")
 import("//testing/test.gni")
 import("//third_party/pdfium/pdfium.gni")
 
-assert(enable_pdf)
-
-pdf_engine = 0  # 0 PDFium
-
-static_library("pdf") {
-  deps = [
-    "//base",
-    "//gin",
-    "//net",
-    "//ppapi/cpp:objects",
-    "//ppapi/cpp/private:internal_module",
-    "//ui/base",
-  ]
+# Generate a buildflag header for compile-time checking of PDF support.
+buildflag_header("features") {
+  header = "features.h"
+  flags = [ "ENABLE_PDF=$enable_pdf" ]
+}
 
-  sources = [
-    "chunk_stream.cc",
-    "chunk_stream.h",
-    "document_loader.cc",
-    "document_loader.h",
-    "draw_utils.cc",
-    "draw_utils.h",
-    "out_of_process_instance.cc",
-    "out_of_process_instance.h",
-    "paint_aggregator.cc",
-    "paint_aggregator.h",
-    "paint_manager.cc",
-    "paint_manager.h",
-    "pdf.cc",
-    "pdf.h",
-    "pdf_engine.h",
-    "preview_mode_client.cc",
-    "preview_mode_client.h",
-  ]
+if (enable_pdf) {
+  pdf_engine = 0  # 0 PDFium
 
-  if (pdf_engine == 0) {
-    deps += [
-      "//pdf/pdfium/fuzzers",
-      "//third_party/pdfium",
+  static_library("pdf") {
+    deps = [
+      "//base",
+      "//gin",
+      "//net",
+      "//ppapi/cpp:objects",
+      "//ppapi/cpp/private:internal_module",
+      "//ui/base",
     ]
 
-    sources += [
-      "pdfium/pdfium_api_string_buffer_adapter.cc",
-      "pdfium/pdfium_api_string_buffer_adapter.h",
-      "pdfium/pdfium_assert_matching_enums.cc",
-      "pdfium/pdfium_engine.cc",
-      "pdfium/pdfium_engine.h",
-      "pdfium/pdfium_mem_buffer_file_read.cc",
-      "pdfium/pdfium_mem_buffer_file_read.h",
-      "pdfium/pdfium_mem_buffer_file_write.cc",
-      "pdfium/pdfium_mem_buffer_file_write.h",
-      "pdfium/pdfium_page.cc",
-      "pdfium/pdfium_page.h",
-      "pdfium/pdfium_range.cc",
-      "pdfium/pdfium_range.h",
+    sources = [
+      "chunk_stream.cc",
+      "chunk_stream.h",
+      "document_loader.cc",
+      "document_loader.h",
+      "draw_utils.cc",
+      "draw_utils.h",
+      "out_of_process_instance.cc",
+      "out_of_process_instance.h",
+      "paint_aggregator.cc",
+      "paint_aggregator.h",
+      "paint_manager.cc",
+      "paint_manager.h",
+      "pdf.cc",
+      "pdf.h",
+      "pdf_engine.h",
+      "preview_mode_client.cc",
+      "preview_mode_client.h",
     ]
-  }
 
-  defines = [ "PDFIUM_PRINT_TEXT_WITH_GDI" ]
-  if (pdf_enable_xfa) {
-    defines += [ "PDF_ENABLE_XFA" ]
+    if (pdf_engine == 0) {
+      deps += [
+        "//pdf/pdfium/fuzzers",
+        "//third_party/pdfium",
+      ]
+
+      sources += [
+        "pdfium/pdfium_api_string_buffer_adapter.cc",
+        "pdfium/pdfium_api_string_buffer_adapter.h",
+        "pdfium/pdfium_assert_matching_enums.cc",
+        "pdfium/pdfium_engine.cc",
+        "pdfium/pdfium_engine.h",
+        "pdfium/pdfium_mem_buffer_file_read.cc",
+        "pdfium/pdfium_mem_buffer_file_read.h",
+        "pdfium/pdfium_mem_buffer_file_write.cc",
+        "pdfium/pdfium_mem_buffer_file_write.h",
+        "pdfium/pdfium_page.cc",
+        "pdfium/pdfium_page.h",
+        "pdfium/pdfium_range.cc",
+        "pdfium/pdfium_range.h",
+      ]
+    }
+
+    defines = [ "PDFIUM_PRINT_TEXT_WITH_GDI" ]
+    if (pdf_enable_xfa) {
+      defines += [ "PDF_ENABLE_XFA" ]
+    }
   }
-}
 
-test("pdf_unittests") {
-  sources = [
-    "chunk_stream_unittest.cc",
-    "run_all_unittests.cc",
-  ]
+  test("pdf_unittests") {
+    sources = [
+      "chunk_stream_unittest.cc",
+      "run_all_unittests.cc",
+    ]
 
-  deps = [
-    ":pdf",
-    "//base",
-    "//base/test:test_support",
-    "//ppapi/c",
-    "//ppapi/cpp",
-    "//testing/gmock",
-    "//testing/gtest",
-  ]
+    deps = [
+      ":pdf",
+      "//base",
+      "//base/test:test_support",
+      "//ppapi/c",
+      "//ppapi/cpp",
+      "//testing/gmock",
+      "//testing/gtest",
+    ]
+  }
+} else {
+  # Dummy group when PDF support is disabled so targets can unconditionally
+  # depend on it.
+  group("pdf") {
+  }
 }