Expose GpuMemoryBufferId through glGetImageivCHROMIUM.

third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp

Index: third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
index 13efb128ed04290fa71be195e82336d98328502a..f8ea5f0f47df002f98d8e050a42cf033f04df66d 100644
--- a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
+++ b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
@@ -934,6 +934,7 @@ void DrawingBuffer::deleteChromiumImageForTexture(TextureInfo* info)
         m_gl->ReleaseTexImage2DCHROMIUM(info->parameters.target, info->imageId);
         m_gl->DestroyImageCHROMIUM(info->imageId);
         info->imageId = 0;
+        info->gpuMemoryBufferId = -1;
     }
 }
 
@@ -972,10 +973,14 @@ DrawingBuffer::TextureInfo DrawingBuffer::createTextureAndAllocateMemory(const I
 
     GLuint textureId = createColorTexture(parameters);
     m_gl->BindTexImage2DCHROMIUM(parameters.target, imageId);
+    GLint gpuMemoryBufferId = -1;
+    m_gl->GetImageivCHROMIUM(imageId, GC3D_GPU_MEMORY_BUFFER_ID, &gpuMemoryBufferId);

[Ken Russell (switch to Gerrit), 2016/05/27 01:02:10]

Questions:

1. Does glGetImageivCHROMIUM require a round-trip to the GPU process, or is it
handled entirely client-side?
2. It looks like when the compositor calls DrawingBuffer::mailboxReleased, the
MailboxInfo contains the previously-queried GPU_MEMORY_BUFFER_ID, so it doesn't
need to be queried again unless the canvas has changed size. Correct? So in the
steady state we are not making this call every frame?

[erikchen, 2016/05/27 01:13:37]

The GMB id is cached client side.
That's correct. The only time we make this call is immediately after
CreateGpuMemoryBufferImageCHROMIUM.

+    DCHECK_NE(-1, gpuMemoryBufferId);
 
     TextureInfo info;
     info.textureId = textureId;
     info.imageId = imageId;
+    info.gpuMemoryBufferId = gpuMemoryBufferId;
     info.parameters = parameters;
     clearChromiumImageAlpha(info);
     return info;
@@ -1002,6 +1007,12 @@ void DrawingBuffer::resizeTextureMemory(TextureInfo* info, const IntSize& size)
         if (info->imageId) {
             m_gl->BindTexture(info->parameters.target, info->textureId);
             m_gl->BindTexImage2DCHROMIUM(info->parameters.target, info->imageId);
+
+            GLint gpuMemoryBufferId = -1;
+            m_gl->GetImageivCHROMIUM(info->imageId, GC3D_GPU_MEMORY_BUFFER_ID, &gpuMemoryBufferId);
+            DCHECK_NE(-1, gpuMemoryBufferId);
+            info->gpuMemoryBufferId = gpuMemoryBufferId;
+
             clearChromiumImageAlpha(*info);
             return;
         }