enable -Wstring-conversion when compiling with clang

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 12e9e64448d1c194c849f0274106c0216f13749f..4685640518483952f4f39e8eb17c72008070604b 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -2804,6 +2804,9 @@
               # Warns on switches on enums that cover all enum values but
               # also contain a default: branch. Chrome is full of that.
               '-Wno-covered-switch-default',
+
+              # Warns when a const char[] is converted to bool.
+              '-Wstring-conversion',
             ],
             'cflags!': [
               # Clang doesn't seem to know know this flag.
@@ -3388,6 +3391,9 @@
                 # Warns on switches on enums that cover all enum values but
                 # also contain a default: branch. Chrome is full of that.
                 '-Wno-covered-switch-default',
+
+                # Warns when a const char[] is converted to bool.
+                '-Wstring-conversion',
               ],
               'OTHER_CPLUSPLUSFLAGS': [
                 # gnu++11 instead of c++11 so that __ANSI_C__ doesn't get