Replace all instances of 'clear' with 'pop's in conical gradient pdf impl, looks like the pdf spec doesn't support Postscript's 'clear' stack operator. Should fix some warnings on mac buildbots.

git-svn-id: http://skia.googlecode.com/svn/trunk@4521 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/pdf/SkPDFShader.cpp b/src/pdf/SkPDFShader.cpp
index edb704d..cbbf5c6 100644
--- a/src/pdf/SkPDFShader.cpp
+++ b/src/pdf/SkPDFShader.cpp
@@ -321,7 +321,7 @@
         function.append(" add\n");
 
         // if r(t) < 0, then it's outside the cone
-        function.append("0 lt {clear false} {true} ifelse\n");
+        function.append("0 lt {pop false} {true} ifelse\n");
 
     } else {
 
@@ -368,11 +368,11 @@
         function.append(" add\n");
 
         // if r(t) < 0, push false, otherwise the smaller root is our t
-        function.append("0 le {clear false} {true} ifelse\n");
+        function.append("0 le {pop false} {true} ifelse\n");
         function.append("} ifelse\n");
 
         // d < 0, clear the stack and push false
-        function.append("} {clear false} ifelse\n");
+        function.append("} {pop pop pop false} ifelse\n");
     }
 
     // if the pixel is in the cone, proceed to compute a color