content: make theme_color more resilient to casting issues

content/public/common/manifest.cc

Index: content/public/common/manifest.cc
diff --git a/content/public/common/manifest.cc b/content/public/common/manifest.cc
index ed19c470073b435008580c28e83da985666b65bb..dc663cfaceb13bbb8241c14e5e54167dfd5c33b6 100644
--- a/content/public/common/manifest.cc
+++ b/content/public/common/manifest.cc
@@ -7,7 +7,12 @@
 namespace content {
 
 const double Manifest::Icon::kDefaultDensity = 1;
-const int64_t Manifest::kInvalidOrMissingThemeColor = -1;
+// We need to provide a value here which is out of the range of a 32-bit integer
+// since otherwise we would not be able to check whether a theme color was valid
+// or not. The simplest way to do this is to simply add one to the maximum
+// possible 32-bit integer.
+const int64_t Manifest::kInvalidOrMissingThemeColor =
+    static_cast<int64_t>(std::numeric_limits<int32_t>::max()) + 1;
 const size_t Manifest::kMaxIPCStringLength = 4 * 1024;
 
 Manifest::Icon::Icon()