enable -Wstring-conversion when compiling with clang

chrome/browser/renderer_host/web_cache_manager_unittest.cc

Index: chrome/browser/renderer_host/web_cache_manager_unittest.cc
diff --git a/chrome/browser/renderer_host/web_cache_manager_unittest.cc b/chrome/browser/renderer_host/web_cache_manager_unittest.cc
index 4d82178785d6f5a85184a4a0ad3ecca206dd76d7..80f1716e6118c56a5ce77640a6c2ec8487e58560 100644
--- a/chrome/browser/renderer_host/web_cache_manager_unittest.cc
+++ b/chrome/browser/renderer_host/web_cache_manager_unittest.cc
@@ -256,7 +256,7 @@ TEST_F(WebCacheManagerTest, AttemptTacticTest) {
     else if (iter->first == kRendererID2)
       EXPECT_LE(kStats2.liveSize, iter->second);
     else
-      EXPECT_FALSE("Unexpected entry in strategy");
+      ADD_FAILURE();   // Unexpected entry in strategy.
     ++iter;
   }
 
@@ -296,7 +296,7 @@ TEST_F(WebCacheManagerTest, AddToStrategyTest) {
     else if (iter->first == kRendererID2)
       EXPECT_LE(kStats2.liveSize + kStats2.deadSize, iter->second);
     else
-      EXPECT_FALSE("Unexpected entry in strategy");
+      ADD_FAILURE();  // Unexpected entry in strategy.
     ++iter;
   }