Disable new clang warning -Wno-enum-enum-conversion in blink build

Change-Id: Ia1f87b0479a92d9f57d4261379044baa13f574b6
Bug: 1035171
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1974530Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Amy Huang <akhuang@google.com>
Cr-Commit-Position: refs/heads/master@{#726116}

build/config/compiler/BUILD.gn

@@ -1545,8 +1545,6 @@ config("default_warnings") {
           cflags += [
             # TODO(https://crbug.com/1031169): Clean up and enable.
             "-Wno-misleading-indentation",
-            # TODO(https://crbug.com/1035171): Clean up and enable.
-            "-Wno-enum-enum-conversion",
           ]
         }
       }

third_party/blink/renderer/BUILD.gn

@@ -48,6 +48,12 @@ config("inside_blink") {
       "-Wno-implicit-float-conversion",
       "-Wno-implicit-int-conversion",
     ]
+
+    if (llvm_force_head_revision) {
+      cflags += [
+        "-Wno-enum-enum-conversion",
+      ]
+    }
   }
 }