Update from https://crrev.com/311076

base/test/expectations/expectation.cc

Index: base/test/expectations/expectation.cc
diff --git a/base/test/expectations/expectation.cc b/base/test/expectations/expectation.cc
index 9b06e282f27a2e56fa7f6749b9fd3635d0669d22..30817791dd2da22d4f612c0959cd0864ae3f9a6c 100644
--- a/base/test/expectations/expectation.cc
+++ b/base/test/expectations/expectation.cc
@@ -38,7 +38,7 @@ static bool IsValidPlatform(const Platform* platform) {
   const std::string& variant = platform->variant;
 
   if (name == "Win") {
-    if (variant != "" &&
+    if (!variant.empty() &&
         variant != "XP" &&
         variant != "Vista" &&
         variant != "7" &&
@@ -46,7 +46,7 @@ static bool IsValidPlatform(const Platform* platform) {
       return false;
     }
   } else if (name == "Mac") {
-    if (variant != "" &&
+    if (!variant.empty() &&
         variant != "10.6" &&
         variant != "10.7" &&
         variant != "10.8" &&
@@ -55,7 +55,7 @@ static bool IsValidPlatform(const Platform* platform) {
       return false;
     }
   } else if (name == "Linux") {
-    if (variant != "" &&
+    if (!variant.empty() &&
         variant != "32" &&
         variant != "64") {
       return false;