Move a bunch of code out of testing/test_support.h.

They should either go into testing/utils/file_util.h,
testing/free_deleter.h, or testing/fx_string_testhelpers.h.
Then do IWYU and remove all the unnecessary test_support.h includes.

Change-Id: Idae09a08b96e2bc0b95ac1820ff305cdfa3f4e1a
Reviewed-on: https://pdfium-review.googlesource.com/c/49930
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/testing/embedder_test_timer_handling_delegate.h b/testing/embedder_test_timer_handling_delegate.h
index 34b4cbb..a32ad202 100644
--- a/testing/embedder_test_timer_handling_delegate.h
+++ b/testing/embedder_test_timer_handling_delegate.h
@@ -11,7 +11,7 @@
 #include <vector>
 
 #include "testing/embedder_test.h"
-#include "testing/test_support.h"
+#include "testing/fx_string_testhelpers.h"
 
 class EmbedderTestTimerHandlingDelegate final : public EmbedderTest::Delegate {
  public: