Add Log.h to replace all uses of iostream

On Android iostream doesn't appear in logcat, the system log that's
often used for printf debugging. Introduce Chromium/ANGLE like logging
that looks like the following:

  InfoLog() << stuff << stuff;

This makes sure the message is put in logcat on Android and removes
static initializers from <iostream>

BUG=dawn:286

Change-Id: Ie0d018f49bcac1a7b740739a6e59d45ae6728638
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/14102
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: David Turner <digit@google.com>
Reviewed-by: Austin Eng <enga@chromium.org>

src/dawn_native/Instance.cpp

@@ -15,10 +15,9 @@
 #include "dawn_native/Instance.h"
 
 #include "common/Assert.h"
+#include "common/Log.h"
 #include "dawn_native/ErrorData.h"
 
-#include <iostream>
-
 namespace dawn_native {
 
     // Forward definitions of each backend's "Connect" function that creates new BackendConnection.
@@ -168,7 +167,7 @@ namespace dawn_native {
             ErrorData* error = maybeError.AcquireError();
 
             ASSERT(error != nullptr);
-            std::cout << error->GetMessage() << std::endl;
+            InfoLog() << error->GetMessage();
             delete error;
 
             return true;