Cherry-pick to XFA: Fix some clang warnings with -Wmissing-braces in pdfium.

Clang warns if there are missing braces around a subobject
initializer. The most common idiom that triggers this is:
  STRUCT s = {0};
if the first field of STRUCT is itself a struct. This can
be more simply written as:
  STRUCT s = {};
which also prevents the warning from firing.

Other instances of the warning have been fixed by adding
braces where appropriate.

R=brucedawson@chromium.org

Review URL: https://codereview.chromium.org/1213523004.
diff --git a/third_party/BUILD.gn b/third_party/BUILD.gn
index 549df8a..44d5e75 100644
--- a/third_party/BUILD.gn
+++ b/third_party/BUILD.gn
@@ -95,10 +95,18 @@
 }
 
 source_set("fx_lcms2") {
+  config("fx_lcms2_warnings") {
+    if (is_clang) {
+      # cmslut.cc is sloppy with aggregate initialization. Version 2.7 of this
+      # library doesn't appear to have this problem.
+      cflags = [ "-Wno-missing-braces" ]
+    }
+  }
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [
     "//build/config/compiler:no_chromium_code",
     "//third_party/pdfium:pdfium_config",
+    ":fx_lcms2_warnings",
   ]
   sources = [
     "lcms2-2.6/include/lcms2.h",
diff --git a/third_party/third_party.gyp b/third_party/third_party.gyp
index ff65771..98ec814 100644
--- a/third_party/third_party.gyp
+++ b/third_party/third_party.gyp
@@ -137,6 +137,11 @@
           ],
         }],
       ],
+      'variables': {
+        'clang_warning_flags': [
+          '-Wno-missing-braces',
+        ],
+      },
     },
     {
       'target_name': 'fx_libjpeg',