Revert of [Fetch API] Start reading blob only when the reader wants to read...

Revert of [Fetch API] Start reading blob only when the reader wants to read contents. (patchset #3 id:40001 of https://codereview.chromium.org/2303753003/ )

Reason for revert:
Speculative revert: this patch is a suspect to cause Linux MSAN failures:

https://uberchromegw.corp.google.com/i/chromium.webkit/builders/WebKit%20Linux%20MSAN/builds/12091

The other suspected patch, the only one related to canvas, was reverted and didn't help.

Original issue's description:
> [Fetch API] Start reading blob only when the reader wants to read contents.
>
> BUG=643174
>
> Committed: https://crrev.com/f1ca96c413912ff1768e4274b8b7ac78eb41de64
> Cr-Commit-Position: refs/heads/master@{#416923}

TBR=hiroshige@chromium.org,jkarlin@chromium.org,yhirano@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=643174

Review-Url: https://codereview.chromium.org/2319093004
Cr-Commit-Position: refs/heads/master@{#417338}

third_party/WebKit/Source/modules/fetch/FetchBlobDataConsumerHandle.cpp

@@ -194,12 +194,12 @@ public:
         {
             if (m_readerContext->drained())
                 return Done;
+            m_readerContext->ensureStartLoader();
             Result r = m_reader->read(data, size, flags, readSize);
             if (!(size == 0 && (r == Ok || r == ShouldWait))) {
                 // We read non-empty data, so we cannot use the blob data
                 // handle which represents the whole data.
                 m_readerContext->clearBlobDataHandleForDrain();
-                m_readerContext->ensureStartLoader();
             }
             return r;
         }

third_party/WebKit/Source/modules/fetch/FetchBlobDataConsumerHandleTest.cpp

@@ -112,9 +112,8 @@ TEST_F(FetchBlobDataConsumerHandleTest, CreateLoader)
         = FetchBlobDataConsumerHandle::create(&document(), blobDataHandle, factory);
     testing::runPendingTasks();
 
-    char buffer[1];
     size_t size = 0;
-    ASSERT_EQ(kShouldWait, handle->obtainReader(nullptr)->read(buffer, sizeof(buffer), kNone, &size));
+    handle->obtainReader(nullptr)->read(nullptr, 0, kNone, &size);
     checkpoint.Call(1);
     testing::runPendingTasks();
     checkpoint.Call(2);
@@ -135,27 +134,6 @@ TEST_F(FetchBlobDataConsumerHandleTest, CreateLoader)
     EXPECT_EQ(NotCORSEnabled, resourceLoaderOptions.corsEnabled);
 }
 
-TEST_F(FetchBlobDataConsumerHandleTest, ZeroByteReadDoesNotCreateLoader)
-{
-    auto factory = new StrictMock<MockLoaderFactory>;
-    Checkpoint checkpoint;
-
-    InSequence s;
-    EXPECT_CALL(checkpoint, Call(1));
-    EXPECT_CALL(checkpoint, Call(2));
-
-    RefPtr<BlobDataHandle> blobDataHandle = createBlobDataHandle("Once upon a time");
-    std::unique_ptr<WebDataConsumerHandle> handle
-        = FetchBlobDataConsumerHandle::create(&document(), blobDataHandle, factory);
-    testing::runPendingTasks();
-
-    size_t size = 0;
-    ASSERT_EQ(kShouldWait, handle->obtainReader(nullptr)->read(nullptr, 0, kNone, &size));
-    checkpoint.Call(1);
-    testing::runPendingTasks();
-    checkpoint.Call(2);
-}
-
 TEST_F(FetchBlobDataConsumerHandleTest, CancelLoaderWhenStopped)
 {
     auto factory = new StrictMock<MockLoaderFactory>;
@@ -176,9 +154,8 @@ TEST_F(FetchBlobDataConsumerHandleTest, CancelLoaderWhenStopped)
         = FetchBlobDataConsumerHandle::create(&document(), blobDataHandle, factory);
     testing::runPendingTasks();
 
-    char buffer[1];
     size_t size = 0;
-    ASSERT_EQ(kShouldWait, handle->obtainReader(nullptr)->read(buffer, sizeof(buffer), kNone, &size));
+    handle->obtainReader(nullptr)->read(nullptr, 0, kNone, &size);
     checkpoint.Call(1);
     testing::runPendingTasks();
     checkpoint.Call(2);
@@ -208,9 +185,8 @@ TEST_F(FetchBlobDataConsumerHandleTest, CancelLoaderWhenDestinationDetached)
     std::unique_ptr<WebDataConsumerHandle::Reader> reader = handle->obtainReader(nullptr);
     testing::runPendingTasks();
 
-    char buffer[1];
     size_t size = 0;
-    ASSERT_EQ(kShouldWait, reader->read(buffer, sizeof(buffer), kNone, &size));
+    reader->read(nullptr, 0, kNone, &size);
     checkpoint.Call(1);
     testing::runPendingTasks();
     checkpoint.Call(2);
@@ -247,9 +223,8 @@ TEST_F(FetchBlobDataConsumerHandleTest, ReadTest)
     src->add(Command(Command::Wait));
     src->add(Command(Command::Done));
 
-    char buffer[1];
     size_t size = 0;
-    ASSERT_EQ(kShouldWait, handle->obtainReader(nullptr)->read(buffer, sizeof(buffer), kNone, &size));
+    handle->obtainReader(nullptr)->read(nullptr, 0, kNone, &size);
     checkpoint.Call(1);
     testing::runPendingTasks();
     checkpoint.Call(2);
@@ -286,9 +261,8 @@ TEST_F(FetchBlobDataConsumerHandleTest, TwoPhaseReadTest)
     src->add(Command(Command::Wait));
     src->add(Command(Command::Done));
 
-    char buffer[1];
     size_t size = 0;
-    ASSERT_EQ(kShouldWait, handle->obtainReader(nullptr)->read(buffer, sizeof(buffer), kNone, &size));
+    handle->obtainReader(nullptr)->read(nullptr, 0, kNone, &size);
     checkpoint.Call(1);
     testing::runPendingTasks();
     checkpoint.Call(2);
@@ -317,9 +291,8 @@ TEST_F(FetchBlobDataConsumerHandleTest, LoadErrorTest)
     std::unique_ptr<WebDataConsumerHandle> handle
         = FetchBlobDataConsumerHandle::create(&document(), blobDataHandle, factory);
 
-    char buffer[1];
     size_t size = 0;
-    ASSERT_EQ(kShouldWait, handle->obtainReader(nullptr)->read(buffer, sizeof(buffer), kNone, &size));
+    handle->obtainReader(nullptr)->read(nullptr, 0, kNone, &size);
     checkpoint.Call(1);
     testing::runPendingTasks();
     checkpoint.Call(2);
@@ -353,9 +326,8 @@ TEST_F(FetchBlobDataConsumerHandleTest, BodyLoadErrorTest)
     src->add(Command(Command::Data, "hello, "));
     src->add(Command(Command::Error));
 
-    char buffer[1];
     size_t size = 0;
-    ASSERT_EQ(kShouldWait, handle->obtainReader(nullptr)->read(buffer, sizeof(buffer), kNone, &size));
+    handle->obtainReader(nullptr)->read(nullptr, 0, kNone, &size);
     checkpoint.Call(1);
     testing::runPendingTasks();
     checkpoint.Call(2);

third_party/WebKit/Source/modules/fetch/FetchFormDataConsumerHandleTest.cpp

@@ -401,6 +401,7 @@ TEST_F(FetchFormDataConsumerHandleTest, ZeroByteReadDoesNotAffectDrainingForComp
     size_t readSize;
     EXPECT_EQ(kShouldWait, reader->read(nullptr, 0, kNone, &readSize));
     testing::runPendingTasks();
+    EXPECT_EQ(kOk, reader->read(nullptr, 0, kNone, &readSize));
     RefPtr<EncodedFormData> formData = reader->drainAsFormData();
     ASSERT_TRUE(formData);
     EXPECT_TRUE(formData->isSafeToSendToAnotherThread());