aw: Fix clearing FBO in External Stencil with viz

This CL restores GL state to correct values before clearing FBO to
ensure glClear happens. It also fixes problem in destruction when
GLContext got destroyed before AwGLSurfaceExternalStencil.

Bug: 1056655

Change-Id: I70102fae19d25ae9d2795ddf37e0c393dc2e18f5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2075971Reviewed-by: Jonathan Backer <backer@chromium.org>
Commit-Queue: Vasiliy Telezhnikov <vasilyt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#745100}

android_webview/browser/gfx/aw_gl_surface_external_stencil.cc

@@ -116,6 +116,8 @@ class AwGLSurfaceExternalStencil::FrameBuffer {
 
   void Clear() {
     glBindFramebufferEXT(GL_FRAMEBUFFER, frame_buffer_object_);
+    glDisable(GL_SCISSOR_TEST);
+    glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
     glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
     glClear(GL_COLOR_BUFFER_BIT);
   }
@@ -219,6 +221,9 @@ gfx::SwapResult AwGLSurfaceExternalStencil::SwapBuffers(
     // We draw only inside clip rect, no need to scissor.
     glDisable(GL_SCISSOR_TEST);
 
+    // Restore color mask in case.
+    glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
+
     glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
   }
 

android_webview/browser/gfx/output_surface_provider_webview.cc

@@ -56,7 +56,12 @@ OutputSurfaceProviderWebview::OutputSurfaceProviderWebview() {
 
   InitializeContext();
 }
-OutputSurfaceProviderWebview::~OutputSurfaceProviderWebview() = default;
+OutputSurfaceProviderWebview::~OutputSurfaceProviderWebview() {
+  // We must to destroy |gl_surface_| before |shared_context_state_|, so we will
+  // still have context. NOTE: |shared_context_state_| holds ref to surface, but
+  // it loses it before context.
+  gl_surface_.reset();
+}
 
 void OutputSurfaceProviderWebview::InitializeContext() {
   DCHECK(!gl_surface_) << "InitializeContext() called twice";