add options to enable/disable "FAILED to read ..." message

--disable-missing-warning
--enable-missing-warning

default is still enabled



git-svn-id: http://skia.googlecode.com/svn/trunk@3992 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gm/gmmain.cpp b/gm/gmmain.cpp
index 7185a73..66cbc0c 100644
--- a/gm/gmmain.cpp
+++ b/gm/gmmain.cpp
@@ -52,6 +52,9 @@
 const static ErrorBitfield ERROR_READING_REFERENCE_IMAGE = 0x08;
 const static ErrorBitfield ERROR_WRITING_REFERENCE_IMAGE = 0x10;
 
+// If true, emit a messange when we can't find a reference image to compare
+static bool gNotifyMissingReadReference;
+
 using namespace skiagm;
 
 class Iter {
@@ -450,7 +453,9 @@
                                           orig, diffPath,
                                           renderModeDescriptor);
     } else {
-        fprintf(stderr, "FAILED to read %s\n", path.c_str());
+        if (gNotifyMissingReadReference) {
+            fprintf(stderr, "FAILED to read %s\n", path.c_str());
+        }
         return ERROR_READING_REFERENCE_IMAGE;
     }
 }
@@ -737,6 +742,8 @@
     bool doDeferred = true;
     bool disableTextureCache = false;
 
+    gNotifyMissingReadReference = true;
+
     const char* const commandName = argv[0];
     char* const* stop = argv + argc;
     for (++argv; argv < stop; ++argv) {
@@ -768,6 +775,10 @@
             doPDF = false;
         } else if (strcmp(*argv, "--nodeferred") == 0) {
             doDeferred = false;
+        } else if (strcmp(*argv, "--disable-missing-warning") == 0) {
+            gNotifyMissingReadReference = false;
+        } else if (strcmp(*argv, "--enable-missing-warning") == 0) {
+            gNotifyMissingReadReference = true;
         } else if (strcmp(*argv, "--serialize") == 0) {
             doSerialize = true;
         } else if (strcmp(*argv, "--match") == 0) {