BufferedDataSource: don't reallocate buffer unnecessarily

When buffer size is different than kInitialReadBufferSize then
intermediate buffer would be reallocated on each Read() operation
which is unnecessary.

Review URL: https://codereview.chromium.org/594733004

Cr-Commit-Position: refs/heads/master@{#296469}

media/blink/buffered_data_source.cc

@@ -90,8 +90,7 @@ BufferedDataSource::BufferedDataSource(
       total_bytes_(kPositionNotSpecified),
       streaming_(false),
       frame_(frame),
-      intermediate_read_buffer_(new uint8[kInitialReadBufferSize]),
-      intermediate_read_buffer_size_(kInitialReadBufferSize),
+      intermediate_read_buffer_(kInitialReadBufferSize),
       render_task_runner_(task_runner),
       stop_signal_received_(false),
       media_has_played_(false),
@@ -314,14 +313,14 @@ void BufferedDataSource::ReadInternal() {
 
   // First we prepare the intermediate read buffer for BufferedResourceLoader
   // to write to.
-  if (size > intermediate_read_buffer_size_) {
-    intermediate_read_buffer_.reset(new uint8[size]);
-  }
+  if (static_cast<int>(intermediate_read_buffer_.size()) < size)
+    intermediate_read_buffer_.resize(size);
 
   // Perform the actual read with BufferedResourceLoader.
+  DCHECK(!intermediate_read_buffer_.empty());
   loader_->Read(position,
                 size,
-                intermediate_read_buffer_.get(),
+                &intermediate_read_buffer_[0],
                 base::Bind(&BufferedDataSource::ReadCallback,
                            weak_factory_.GetWeakPtr()));
 }
@@ -448,7 +447,8 @@ void BufferedDataSource::ReadCallback(
   }
 
   if (bytes_read > 0) {
-    memcpy(read_op_->data(), intermediate_read_buffer_.get(), bytes_read);
+    DCHECK(!intermediate_read_buffer_.empty());
+    memcpy(read_op_->data(), &intermediate_read_buffer_[0], bytes_read);
   } else if (bytes_read == 0 && total_bytes_ == kPositionNotSpecified) {
     // We've reached the end of the file and we didn't know the total size
     // before. Update the total size so Read()s past the end of the file will

media/blink/buffered_data_source.h

@@ -6,6 +6,7 @@
 #define MEDIA_BLINK_BUFFERED_DATA_SOURCE_H_
 
 #include <string>
+#include <vector>
 
 #include "base/callback.h"
 #include "base/memory/scoped_ptr.h"
@@ -196,8 +197,7 @@ class MEDIA_EXPORT BufferedDataSource : public DataSource {
   // because we want buffer to be passed into BufferedResourceLoader to be
   // always non-null. And by initializing this member with a default size we can
   // avoid creating zero-sized buffered if the first read has zero size.
-  scoped_ptr<uint8[]> intermediate_read_buffer_;
-  int intermediate_read_buffer_size_;
+  std::vector<uint8> intermediate_read_buffer_;
 
   // The task runner of the render thread.
   const scoped_refptr<base::SingleThreadTaskRunner> render_task_runner_;