Add test for SpdyReadQueue::Clear().

* Zero out |total_size_| member in SpdyReadQueue::Clear(), otherwise the next
  call to IsEmpty() would crash.
* Add test for SpdyReadQueue::Clear().
* Add a comment to document class invariant.
* Move SpdyReadQueue tests into namespace test.

This is a follow-up to
https://crrev.com/2386883002/diff/40001/net/spdy/spdy_read_queue.cc#newcode53

Review-Url: https://codereview.chromium.org/2388243003
Cr-Commit-Position: refs/heads/master@{#422875}

net/spdy/spdy_read_queue.cc

@@ -53,6 +53,7 @@ size_t SpdyReadQueue::Dequeue(char* out, size_t len) {
 
 void SpdyReadQueue::Clear() {
   queue_.clear();
+  total_size_ = 0;
 }
 
 }  // namespace net

net/spdy/spdy_read_queue.h

@@ -40,6 +40,8 @@ class NET_EXPORT_PRIVATE SpdyReadQueue {
   void Clear();
 
  private:
+  // Class invariant:
+  // |total_size_| is the sum of GetRemainingSize() of |queue_|'s elements.
   std::deque<std::unique_ptr<SpdyBuffer>> queue_;
   size_t total_size_;
 

net/spdy/spdy_read_queue_unittest.cc

@@ -9,12 +9,14 @@
 #include <memory>
 #include <string>
 
+#include "base/bind.h"
+#include "base/memory/ptr_util.h"
 #include "base/stl_util.h"
 #include "net/spdy/spdy_buffer.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace net {
-
+namespace test {
 namespace {
 
 const char kData[] = "SPDY read queue test data.\0Some more data.";
@@ -84,6 +86,17 @@ void RunEnqueueDequeueTest(size_t enqueue_max_buffer_size,
   EXPECT_EQ(data, drained_data);
 }
 
+void OnBufferDiscarded(bool* discarded,
+                       size_t* discarded_bytes,
+                       size_t delta,
+                       SpdyBuffer::ConsumeSource consume_source) {
+  EXPECT_EQ(SpdyBuffer::DISCARD, consume_source);
+  *discarded = true;
+  *discarded_bytes = delta;
+}
+
+}  // namespace
+
 class SpdyReadQueueTest : public ::testing::Test {};
 
 // Call RunEnqueueDequeueTest() with various buffer size combinatinos.
@@ -101,6 +114,26 @@ TEST_F(SpdyReadQueueTest, CoprimeBufferSizes) {
   RunEnqueueDequeueTest(3, 2);
 }
 
-}  // namespace
+TEST_F(SpdyReadQueueTest, Clear) {
+  auto buffer = base::MakeUnique<SpdyBuffer>(kData, kDataSize);
+  bool discarded = false;
+  size_t discarded_bytes = 0;
+  buffer->AddConsumeCallback(
+      base::Bind(&OnBufferDiscarded, &discarded, &discarded_bytes));
+
+  SpdyReadQueue read_queue;
+  read_queue.Enqueue(std::move(buffer));
+
+  EXPECT_FALSE(discarded);
+  EXPECT_EQ(0u, discarded_bytes);
+  EXPECT_FALSE(read_queue.IsEmpty());
+
+  read_queue.Clear();
+
+  EXPECT_TRUE(discarded);
+  EXPECT_EQ(kDataSize, discarded_bytes);
+  EXPECT_TRUE(read_queue.IsEmpty());
+}
 
+}  // namespace test
 }  // namespace net