More adb buffer fixes.

This patch factors out a lot of the basic protocol code: sending OKAY,
sending FAIL, and sending a length-prefixed string.

ADB_TRACE has been non-optional for a long time, so let's just remove
the #ifs.

Also actually build the device tracker test tool (and remove its duplicate).

Bug: http://b/20666660
Change-Id: I6c7d59f18707bdc62ca69dea45547617f9f31fc6
diff --git a/adb/adb_io_test.cpp b/adb/adb_io_test.cpp
index da340b2..dd09919 100644
--- a/adb/adb_io_test.cpp
+++ b/adb/adb_io_test.cpp
@@ -139,13 +139,13 @@
     ASSERT_EQ(ENOSPC, errno);
 }
 
-TEST(io, WriteStringFully) {
+TEST(io, WriteFdExactly_string) {
   const char str[] = "Foobar";
   TemporaryFile tf;
   ASSERT_NE(-1, tf.fd);
 
   // Test writing a partial string to the file.
-  ASSERT_TRUE(WriteStringFully(tf.fd, str)) << strerror(errno);
+  ASSERT_TRUE(WriteFdExactly(tf.fd, str)) << strerror(errno);
   ASSERT_EQ(0, lseek(tf.fd, SEEK_SET, 0));
 
   std::string s;