Set write buffer flags only in SkWriteBuffer and SkFlatController constructors.

This is a baby step toward refactored (and faster in-process) typeface and flattenable factory encoding and decoding.  The sooner SkWriteBuffer knows its flags, the better.

Next steps will be to rearrange Sk{Read,Write}Buffer members into disjoint strategies to handle typefaces and flattenable factories: one for in-process, one for cross-process, one when validating.

BUG=skia:
R=reed@google.com, scroggo@google.com

Author: mtklein@google.com

Review URL: https://codereview.chromium.org/138803005

git-svn-id: http://skia.googlecode.com/svn/trunk@13253 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/tests/SerializationTest.cpp b/tests/SerializationTest.cpp
index 2e02c3e..f35f568 100644
--- a/tests/SerializationTest.cpp
+++ b/tests/SerializationTest.cpp
@@ -110,8 +110,7 @@
 
 template<typename T>
 static void TestObjectSerialization(T* testObj, skiatest::Reporter* reporter) {
-    SkWriteBuffer writer;
-    writer.setFlags(SkWriteBuffer::kValidation_Flag);
+    SkWriteBuffer writer(SkWriteBuffer::kValidation_Flag);
     SerializationUtils<T>::Write(writer, testObj);
     size_t bytesWritten = writer.bytesWritten();
     REPORTER_ASSERT(reporter, SkAlign4(bytesWritten) == bytesWritten);
@@ -141,8 +140,7 @@
 template<typename T>
 static T* TestFlattenableSerialization(T* testObj, bool shouldSucceed,
                                        skiatest::Reporter* reporter) {
-    SkWriteBuffer writer;
-    writer.setFlags(SkWriteBuffer::kValidation_Flag);
+    SkWriteBuffer writer(SkWriteBuffer::kValidation_Flag);
     SerializationUtils<T>::Write(writer, testObj);
     size_t bytesWritten = writer.bytesWritten();
     REPORTER_ASSERT(reporter, SkAlign4(bytesWritten) == bytesWritten);
@@ -180,8 +178,7 @@
 
 template<typename T>
 static void TestArraySerialization(T* data, skiatest::Reporter* reporter) {
-    SkWriteBuffer writer;
-    writer.setFlags(SkWriteBuffer::kValidation_Flag);
+    SkWriteBuffer writer(SkWriteBuffer::kValidation_Flag);
     SerializationUtils<T>::Write(writer, data, kArraySize);
     size_t bytesWritten = writer.bytesWritten();
     // This should write the length (in 4 bytes) and the array