Tell V8 about the extra memory being held by FileReader objects.

third_party/WebKit/Source/core/fileapi/FileReaderLoader.cpp

Index: third_party/WebKit/Source/core/fileapi/FileReaderLoader.cpp
diff --git a/third_party/WebKit/Source/core/fileapi/FileReaderLoader.cpp b/third_party/WebKit/Source/core/fileapi/FileReaderLoader.cpp
index d0e1b24c2d903d35d7c45a57fef9bfe7281ea8a8..653ccd9cc0cbd35c8929a76182abf8fe53460e4a 100644
--- a/third_party/WebKit/Source/core/fileapi/FileReaderLoader.cpp
+++ b/third_party/WebKit/Source/core/fileapi/FileReaderLoader.cpp
@@ -50,6 +50,7 @@
 #include "platform/wtf/text/Base64.h"
 #include "platform/wtf/text/StringBuilder.h"
 #include "public/platform/WebURLRequest.h"
+#include "v8/include/v8.h"
 
 namespace blink {
 
@@ -69,6 +70,7 @@ FileReaderLoader::FileReaderLoader(ReadType read_type,
 
 FileReaderLoader::~FileReaderLoader() {
   Cleanup();
+  UnreportMemoryUsageToV8();
   if (!url_for_reading_.IsEmpty()) {
     BlobRegistry::RevokePublicBlobURL(url_for_reading_);
   }
@@ -143,9 +145,23 @@ void FileReaderLoader::Cleanup() {
     string_result_ = "";
     is_raw_data_converted_ = true;
     decoder_.reset();
+    UnreportMemoryUsageToV8();
   }
 }
 
+void FileReaderLoader::ReportAdditionalMemoryUsageToV8(int64_t usage) {
+  memory_usage_reported_to_v8_ += usage;
+  v8::Isolate::GetCurrent()->AdjustAmountOfExternalAllocatedMemory(usage);
+}
+
+void FileReaderLoader::UnreportMemoryUsageToV8() {
+  if (!memory_usage_reported_to_v8_)
+    return;
+  v8::Isolate::GetCurrent()->AdjustAmountOfExternalAllocatedMemory(
+      -memory_usage_reported_to_v8_);
+  memory_usage_reported_to_v8_ = 0;
+}
+
 void FileReaderLoader::DidReceiveResponse(
     unsigned long,
     const ResourceResponse& response,
@@ -230,6 +246,7 @@ void FileReaderLoader::DidReceiveData(const char* data, unsigned data_length) {
   }
   bytes_loaded_ += bytes_appended;
   is_raw_data_converted_ = false;
+  ReportAdditionalMemoryUsageToV8(bytes_appended);
 
   if (client_)
     client_->DidReceiveData();
@@ -332,6 +349,8 @@ String FileReaderLoader::StringResult() {
       NOTREACHED();
   }
 
+  if (finished_loading_)

[dmurph, 2017/04/27 21:57:12]

To make this more clear, can you have the two Convert methods return the string,
which you then std::move into string_result_?

Then it makes more sense in this method that you're allocating that memory right
now, and you want to report it.


Then, if we're finished loading:
* clear raw_data_.
* int64_t size_diff = string_result_.size() - memory_usage_reported_to_v8_;
  AdjustAdditionalV8MemoryUsage(size_diff).

That makes the memory amount accurate, and we clear raw_data_ (which it looks
like we're hanging on to for some reason).

[michaeln, 2017/04/28 00:54:25]

ok, i made it more accurate and thnx for pointing out that we don't need to hang
onto raw_data_ beyond this point

+    ReportAdditionalMemoryUsageToV8(string_result_.CharactersSizeInBytes());
   return string_result_;
 }