Remove 'String::append' from some of the blink source.

Source/platform/graphics/filters/custom/CustomFilterValidatedProgram.cpp

Index: Source/platform/graphics/filters/custom/CustomFilterValidatedProgram.cpp
diff --git a/Source/platform/graphics/filters/custom/CustomFilterValidatedProgram.cpp b/Source/platform/graphics/filters/custom/CustomFilterValidatedProgram.cpp
old mode 100644
new mode 100755
index 63e384383be80e8541611155a126ce7e32294f9e..1e03309de7a8ebd1fec0e1c1c4b701768f7789af
--- a/Source/platform/graphics/filters/custom/CustomFilterValidatedProgram.cpp
+++ b/Source/platform/graphics/filters/custom/CustomFilterValidatedProgram.cpp
@@ -290,7 +290,7 @@ String CustomFilterValidatedProgram::blendFunctionString(blink::WebBlendMode ble
     const char* blendComponentExpression = "Co = 0.0;";
     bool needsLuminosityHelperFunctions = false;
     bool needsSaturationHelperFunctions = false;
-    String blendFunctionString;
+    StringBuilder blendFunctionString;
     switch (blendMode) {
     case blink::WebBlendModeNormal:
         blendColorExpression = "Cs";
@@ -509,7 +509,7 @@ String CustomFilterValidatedProgram::blendFunctionString(blink::WebBlendMode ble
         }
     ), blendComponentExpression, blendColorExpression));
 
-    return blendFunctionString;
+    return blendFunctionString.toString();
 }
 
 String CustomFilterValidatedProgram::compositeFunctionString(CompositeOperator compositeOperator)