Build System: Remove some warning suppression.

For warnings which aren't removed, restrict them to third_party with
the "no_chromium_code" config.

R=jamesr@chromium.org

Review URL: https://codereview.chromium.org/1755843003 .

build/config/compiler/BUILD.gn

diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 45c8e34..da32a26 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -746,7 +746,6 @@
 
   # Disables.
   "-Wno-missing-field-initializers",  # "struct foo f = {0};"
-  "-Wno-unused-parameter",  # Unused function parameters.
 ]
 
 if (is_mac) {
@@ -825,17 +824,6 @@
     # code generated by flex (used in angle) contains that keyword.
     # http://crbug.com/255186
     "-Wno-deprecated-register",
-
-    # TODO(thakis): This used to be implied by -Wno-unused-function,
-    # which we no longer use. Check if it makes sense to remove
-    # this as well. http://crbug.com/316352
-    "-Wno-unneeded-internal-declaration",
-
-    # TODO(thakis): Remove, http://crbug.com/263960
-    "-Wno-reserved-user-defined-literal",
-
-    # TODO(hans): Get this cleaned up.
-    "-Wno-inconsistent-missing-override",
   ]
 
   # NaCl's Clang compiler and Chrome's hermetic Clang compiler will almost
@@ -846,9 +834,6 @@
     default_warning_flags += [
       # TODO(smklein): Enable this, crbug.com/507717
       "-Wno-shift-negative-value",
-
-      # TODO(smklein): Consider enabling this once not broken by third party
-      "-Wno-bitfield-width",
     ]
   }
 }
@@ -919,6 +904,14 @@
       "-Wno-deprecated",
     ]
   }
+
+  if (is_clang) {
+    cflags += [
+      # TODO(hans): Get this cleaned up.
+      "-Wno-inconsistent-missing-override",
+    ]
+  }
+
   cflags += default_warning_flags
   cflags_cc += default_warning_flags_cc
 }