My clang now doesn't complain about !"foo".

BUG=
R=robertphillips@google.com

Review URL: https://codereview.chromium.org/22875037

git-svn-id: http://skia.googlecode.com/svn/trunk@10874 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/pdf/SkPDFUtils.h b/src/pdf/SkPDFUtils.h
index 4f54db6..b30821d 100644
--- a/src/pdf/SkPDFUtils.h
+++ b/src/pdf/SkPDFUtils.h
@@ -27,7 +27,7 @@
 
 #define NOT_IMPLEMENTED(condition, assert)                         \
     do {                                                           \
-        if (condition) {                                           \
+        if ((bool)(condition)) {                                   \
             PRINT_NOT_IMPL("NOT_IMPLEMENTED: " #condition "\n");   \
             SkDEBUGCODE(SkASSERT(!assert);)                        \
         }                                                          \