Disable clang coverage instrumentation for dav1d_10bit.

This should avoid the issue where code coverage instrumentation gets
confused about which of the two copies of the compiled code (dav1d_8bit
vs dav1d_10bit) is executed, and results in counter overflows.

R=mmoroz,dalecurtis@chromium.org,sajjadm,liaoyuke

Bug: 1030350
Change-Id: I8b1c93e27017622022e0562957f1f72cf85eecdc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1951976
Commit-Queue: Roberto Carrillo <robertocn@chromium.org>
Reviewed-by: Max Moroz <mmoroz@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#721787}

third_party/dav1d/BUILD.gn

@@ -184,7 +184,14 @@ static_library("dav1d_8bit") {
 }
 
 static_library("dav1d_10bit") {
-  configs -= [ "//build/config/compiler:chromium_code" ]
+  configs -= [
+    "//build/config/compiler:chromium_code",
+    # Disable coverage for the 10 bit version to avoid confusing the
+    # instrumentation about which version of the library is being run.
+    # dav1d_10 bit was selected for this, as it's less used than dav1d_8bit,
+    # which still has coverage enabled.
+    "//build/config/coverage:default_coverage",
+  ]
   configs += [
     "//build/config/compiler:no_chromium_code",
     ":dav1d_config",