Use PASS() everywhere in ppapi/tests.

ppapi/tests/test_image_data.cc

Index: ppapi/tests/test_image_data.cc
diff --git a/ppapi/tests/test_image_data.cc b/ppapi/tests/test_image_data.cc
index 630026444c1693c69799cf9f438db2e19d9d3f4a..f3df40c02a09f1832168351f202a7094f947fdd2 100644
--- a/ppapi/tests/test_image_data.cc
+++ b/ppapi/tests/test_image_data.cc
@@ -37,7 +37,7 @@ std::string TestImageData::TestInvalidFormat() {
   if (!b.is_null())
     return "Negative image data format accepted";
 
-  return "";
+  PASS();
 }
 
 std::string TestImageData::TestInvalidSize() {
@@ -75,7 +75,7 @@ std::string TestImageData::TestInvalidSize() {
   if (rsrc)
     return "Negative width accepted";
 
-  return "";
+  PASS();
 }
 
 std::string TestImageData::TestHugeSize() {
@@ -83,7 +83,7 @@ std::string TestImageData::TestHugeSize() {
                           pp::Size(100000000, 100000000), true);
   if (!huge_size.is_null())
     return "31-bit overflow size accepted";
-  return "";
+  PASS();
 }
 
 std::string TestImageData::TestInitToZero() {
@@ -111,7 +111,7 @@ std::string TestImageData::TestInitToZero() {
     }
   }
 
-  return "";
+  PASS();
 }
 
 std::string TestImageData::TestIsImageData() {
@@ -135,5 +135,5 @@ std::string TestImageData::TestIsImageData() {
   if (!image_data_interface_->IsImageData(img.pp_resource()))
     return "Image data should be identified as an image";
 
-  return "";
+  PASS();
 }