Reland "Actually enable -Wimplicit-fallthrough for pdfium."

This reverts commit 2388506a1ba13481463033b414f46c1b8864519e.

Reason for revert: Fixed the fallthroughs in XFA and some others.

After the following CLs, I'm pretty confident the errors are
caught in the PDFium bots rather than on Chromium waterfall:

https://pdfium-review.googlesource.com/c/pdfium/+/27010
Roll DEPS for clang to a695c30c.

https://pdfium-review.googlesource.com/c/pdfium/+/26950
Fix fallthroughs in XFA code.

https://pdfium-review.googlesource.com/c/pdfium/+/27050
Fix more fallthroughs before reenabling -Wimplicit-fallthrough.

Original change's description:
> Revert "Actually enable -Wimplicit-fallthrough for pdfium."
>
> This reverts commit 60027a205953e95b230f289118448b55f12f9a94.
>
> Reason for revert: This will break the fuzzer build in Chromium because the XFA side is still broken. I think we need to roll the build/ directory or clang to get the new flag and then build locally before re-enabling?
>
> Or, build with pdf_enable_xfa = true in a chrome checkout.
>
>
> Original change's description:
> > Actually enable -Wimplicit-fallthrough for pdfium.
> >
> > I forgot to do this in https://pdfium-review.googlesource.com/c/pdfium/+/26210
> > which made PDFium compile with the warning enabled.
> >
> > Bug: 807632
> > Change-Id: Id12e3df3073f3b9550d5bc9dfea0068088496f8a
> > Reviewed-on: https://pdfium-review.googlesource.com/26910
> > Reviewed-by: dsinclair <dsinclair@chromium.org>
> > Reviewed-by: Tom Sepez <tsepez@chromium.org>
> > Commit-Queue: Nico Weber <thakis@chromium.org>
>
> TBR=thakis@chromium.org,tsepez@chromium.org,dsinclair@chromium.org
>
> Change-Id: I6bcd6c7aadd43aa0a68b9cd7b1d47e10e2c487ae
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: 807632
> Reviewed-on: https://pdfium-review.googlesource.com/26930
> Reviewed-by: dsinclair <dsinclair@chromium.org>
> Commit-Queue: dsinclair <dsinclair@chromium.org>

TBR=thakis@chromium.org,tsepez@chromium.org,dsinclair@chromium.org

Change-Id: Idbac99ba1e42846cbd84e5eb19cdae67fc1b80a8
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 807632
Reviewed-on: https://pdfium-review.googlesource.com/27091
Commit-Queue: Henrique Nakashima <hnakashima@chromium.org>
Reviewed-by: Henrique Nakashima <hnakashima@chromium.org>

1 files changed, 0 insertions, 4 deletions

diff --git a/BUILD.gn b/BUILD.gn
index f97a195413..d7c8640a2a 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -71,10 +71,6 @@ config("pdfium_common_config") {
     # Assume UTF-8 by default to avoid code page dependencies.
     cflags += [ "/utf-8" ]
   }
-  if (is_clang) {
-    # TODO(thakis): Consider enabling this, https://crbug.com/807632
-    cflags += [ "-Wno-implicit-fallthrough" ]
-  }
 }
 
 config("pdfium_core_config") {